Make a note of your existing hard drive's make and model number - you can get this from Device Manager under Disk Drives, or through HDD Health. Once done, browse to a suitable search engine such as Google or Windows Live and type the make and model into it. If any results are returned, make a note of the following details: drive size (2.5-inch or 3.5-inch), capacity (in GB), interface (SATA or IDE/PATA), speed (in revolutions per minute, or rpm), and cache (in MB).

If you can't find any information online, open your desktop PC and compare the cable that connects the drive to your motherboard with the photo above. If it's connected by a flat ribbon (right), then the drive is IDE/PATA; if it's connected via a narrow cable with a small L-shaped connector (left) then it's a SATA drive.

You'll need to examine the laptop drive itself to see whether it's IDE or SATA. Compare its connectors to the photo above - the top drive is a SATA drive, the bottom one is an IDE drive.

If you've purchased a desktop drive and you have a space in your case to fit it alongside your existing drive, then do so - you'll need a spare 3.5-inch bay to fit the drive into, plus a spare power connector and either SATA cable or IDE ribbon (look for a second connector on an existing ribbon - up to two drives can be connected per ribbon, although your new drive will need to be connected as a slave by changing its jumper settings - check the drive itself or any documentation that came with it for instructions).

If you have a laptop drive, or there's no room for your new desktop drive to be fitted internally, you'll need to install it in an external drive enclosure so you can connect it externally to your PC or laptop via a spare USB or Firewire port. Make sure the enclosure supports your drive's size and interface, plus connects to your PC via a supported medium (typically USB). When it comes to fitting the drive, detailed instructions should be provided, but basically you should just plug the drive into the controller, secure it with the supplied screws and slot it into the casing.

If your new drive didn't come with drive copying software, download EASUS Partition Manager 3.0 Home Edition from one of the links provided here. Once downloaded, double-click epm.zip and drag  EPMSetup from the window that opens on to your desktop, choosing Yes when prompted. Now double-click EPMSetup and follow the instructions to install the program.

Launch EASUS Partition Manager 3.0. You should see both your hard drives represented as bar charts, with your new drive currently showing a single grey bar with the caption "unallocated". As you're copying the entire drive across, you need to click on Disk 1 to highlight it, then click the Disk Copy option under Disk Operations in the left-hand pane.

The Disk Copy Wizard will launch - wait while it performs some analysis on your old drive. Once complete, click Next. A list of available hard drives should appear on-screen - select your new drive from the list and click Next again.

If your new drive is larger than your old drive, you'll be prompted to resize any existing partitions to fit the empty space (marked in grey) as you see fit. If you have a single partition, click and drag on its right-hand frame to allocate the rest of the space to it; if you have two more partitions, you can move the partitions around by clicking and dragging to free up space to their left to allocate to the main system partition.

Read the final instructions and click Finish. Your existing drive will be locked, so all you need to do now is click Apply. Click Yes when prompted, and then click Yes again to allow your PC to reboot during the copy process (make sure any bootable discs are removed from your CD/DVD drive).

Your PC will immediately reboot. After the Windows loading screen has appeared, you'll be given a short period in which to press any key to abort the copy procedure. Press nothing and the progress screen above will appear. Sit back and make yourself a cup of tea (or ten) - the process can take some time.

Once the process is complete, you'll be taken to the Windows desktop, where you may be prompted to reboot again to finish installing new devices. Do so, and then open My Computer to verify the existence of your new drive(s). The capacities may be different, but the contents of each duplicated drive should be the same.

Power down your PC and switch it off at the mains. If swapping an external drive with an internal one, make sure the new drive's jumper settings match the old drive's (Master or Cable Select); if both drives were fitted internally, remove the old drive and set the new drive's jumper to Master.

Shut down your laptop, unplug it from the mains and remove the battery. Now remove your old hard drive as instructed by your laptop manual (check your laptop manufacturer's web site for a servicing guide or manual) and replace it with the new one. You may find the drive has to be separated from a plastic cover of some form, so handle with care. Once complete, restart your PC and Windows should boot, although you may be prompted by the Windows boot menu or have to restart once or twice more to complete the process.