CCleaner is handy for getting rid of registry's from uninstalled games-you can get files left behind.
for example I used to use Norton 360 (big mistake) as AV software as it was an absolute resource hog and slowed it down, so i just switched it off while playing until I switched to Microsoft essentials. but not everyone is comfortable doing that. I also close down Explorer aswell, then just put it back on via task manager when I'm finished playing. Have a look in the processes tab on the task manager and see what you don't need to run. When I first did it I was very surprised by what percentage of memory was used by other programmes. Like right now Google Chrome is using over 128k worth of memory.
Basically the smaller the RAM, the more the processor will struggle. Especially if a laptop is being used that is fairly old. Also Windows 32 bit isn't as good as windows 64 bit as even though you can have more RAM than necessary, not all of it will be available in Win 32 bit (I won't get too technical about that part as it's....technical lol)