what you could try (among a million other things):
- open the task manager (Ctrl-Alt-Delete, "Task manager" button in the popup).
- kill most of the processes in the "processes" tab (right-click, End process tree).
- there are some you shouldn't kill - find by trial and error (explorer is one)
- try if performance is better
- after a reboot, everything is the same as before => little risk to do any damage this way.
a more permanent solution is to go to control panel, "add/remove software". Uninstall everything you don't use.