Have a look at this video from howstuffworks.com - it explains all you need to know about upgrading the RAM in your computer:

A cheap place to buy RAM on the high street? Somewhere like Maplin is a great idea - they are cheaper than PC world, and will allow you to return the part it if is not correct.

Online, somewhere like play.com or insight.com are good - although watch the shipping costs! It often becomes cheaper to buy on the high street when you add that £10.

Jaytag would be happy to assist in adding more RAM to your PC if you are not confident - give us a call on 0845 310 2750.