AnnoyingParrot :
I've only had the computer a few days and all the parts are brand new so I don't really know.
I have the stock heatsink but as soon as i get money I'll buy a water cooler.
It is tightly mounted.
With the stock heatsink you should not have any problems, it should be able to maintain a decent temperature.
I would say go to the computer store get some thermal paste, remove the heatsink and clean off both the CPU and the heatsink (use rubbing alcohol and a tissue). Make sure nothing is stuck to the CPU (plastic wrapping, labels, etc). Then put about a grain of rice worth of thermal paste in the center of the cpu, install the heatsink and hold it in place (do not move or remove it) and lock it down.
Without doing this your computer is unusable at this point.
You do not need a water cooler unless you plan to heavily overclock, any good air cooler such as the CRYORIG H7 will let you overclock somewhat and keeps the CPU very cool.