danielstarrx :
How do i find that out sorry total noob here
If you've bought instead of built your PC, it is more difficult to know what case you have as most of the case used in prebuilts are custom made by manufacturers. I'd suggest you simply take a ruler (that's made of non-conductive material: a plastic one should do) and mesure from the motherboard to the width of inside of the case (that will give you an approximation of how high your CPU cooler can be)
For the motherboard, you can install a software called CPU-Z and go into the "Mainboard" section to get the motherboard's model. What you will want to do, is lookup the motherboard's model online and see what socket it has (a socket will generally be 3 to 4 digits or letters, like 775, 1150, AM3+, etc)
Once you have both informations, you can use websites like Newegg or NCIX and look for CPU coolers and make sure that it can fit on your motherboard's socket and that it isn't too tall for your case.