I was able to reassemble my own pc, and get it working nicely after it messed up. I was so stressed I would break something. But I didn't, and the difference in speed was crazy. I figured out that there were airflow problems, and there was so much dust.
Nice, that feels so good when you solve your own problem like that. I've opened my laptop many times before but I haven't dealt with an actual desktop - I'd have the same fears as you
I feel like I'd be more scared with a laptop, because everything is smaller and more delicate. I don't trust my hands with things that are too intricate.