OK, OP. Here's what you do.
If you have any money at all: first priority is 2gb more RAM, total of 4gb.
You can check what memory's currently installed with the tool "CPU-Z", freely available online. It may have 1x 2gb installed, so you will have to get 1x 2gb, or 2x 1gb in which case you should obviously get 2x 2gb.
Now that's a 32-bit processor so you might only get to use 3.25gb of it but that's still a big improvement.
If you have no cash left after this, skip to final paragraph.
If you have any cash left, get a new HDD and put Win 7 on it. (if the user can handle it, Win 8.1 will feel lighter & faster)
If you have no computer dosh to spend:
1. go on an uninstall spree. Uninstall EVERYTHING that's not Microsoft. Uninstall all the printer drivers, "system utilities", etc. until you have nothing left but windows updates, Visual C++ crap, Silverlight, and maybe Office. You can keep ONE web browser too (that means getting rid of IE if it's not being used, in add/remove windows components). Install Adblock in that browser.
1.1. Replace whatever antivirus you have with MS Security Essentials.
2. Install only what the user really needs.
3. Leave the damn machine alone. Defragging is usually a waste of time. Junk-clean-up is best done by using the Disk Cleanup tool activated automatically by a scheduled task.