For the most part, it's plug and play... if you know where something goes, it plugs in easily.
The most important part is the thermal paste on the CPU... if it isn't done right, you'll fry your CPU. It's very very easy, and you can figure out how to do it correctly by spending 5 minutes on youtube or google, but again, super important. 99% of the time, the "grain of rice" method works best.
Other than that, you just need patience. It's pretty simple and straight forward.
Just look it up on youtube, there will be a million videos on it. You'll do fine and save a ton of money in the process.