There are a few things you can do.
Martin is right, although what I’d do first is look into add/remove programs and clear out anything that they don’t use. Quite often there are programs bundled with the PC that they have never even seen let alone used. Then do the disk clean-up and defragment.
My work laptop started running slowly, mainly because I just have too many things running at the same time as part of my role and this little tip sped it up hugely. It does leave it looking more low tech but for me usability was the most important thing.
To adjust all visual effects for best performance:
Open Performance Information and Tools by clicking the Start button Picture of the Start button, and then clicking Control Panel. In the search box, type Performance Information and Tools, and then, in the list of results, click Performance Information and Tools.
Click Adjust visual effects. Administrator permission required If you’re prompted for an administrator password or confirmation, type the password or provide confirmation.
Click the Visual Effects tab, click Adjust for best performance, and then click OK. (For a less drastic option, select Let Windows choose what’s best for my computer.)