You have a few options that vary in terms of cost and ball ache - a few off the top of my head:
Buy more RAM. Go to
www.crucial.com/uk and run the scanner tool. That will tell you how much you currently have and the max amount the laptop can cope with. Usually dead simple to replace, there is likely to be a small panel on the base that just unscrews.
Buy a SSD. This is a faster type of disk. The biggest performance boost you can give a laptop usually. Means you'll need to reinstall everything which can be a pain.
Reinstall Windows. Is a pain but it will take you back to how it was a year ago without all the crap a PC naturally acquires after a year in use.