I would first carry out a scan of your computer to find out what amount of memory (RAM) you have at the moment.
Use this site
http://www.crucial.com/uk/?click=true
You will then be told how much RAM (random access memory) you have and by what amount you can increase it to.
I recently did the same and it told me I could increase it to 2GB Max.
I purchased two 1GB memory strips of the type Crucial recommended, and put them into my computer myself, not a hard thing to do.
I recommend Crucial they were loads cheaper than the famous high street outlet, and they arrived the very next day.
Hope this helps, I must add however that I did this upgrade on a desktop computer not a laptop, but I shouldn't think it would be any more difficult, perhaps others will tell you.
Incidentally I also purchase an anti static wrist strap, costing �1.99.