Slow computer

[missprim]

My computer is really really slow, it drives me mad.Someone told me I need to buy more memory for it but I was wondering if there was another way I could perhaps get rid of stuff on it that I don't use but don't know how to do this.
it seems the one marked FACTORY_IMAGE (D:) is the one taking up lots of space but it means nothing to me.
If you can explain what I need to do, can you explain it as simple as possible please. Thanks