I did mine for the first time in preparation for FF XIV, and I was a bit nervous being it my first time with no help.
Honestly it wasn't that bad. Taking out cables and plugging in cables related to the MB was the easiest part.
The only part I had a hard time with was removing/cables to the HD because my case has a stupid setup, and I guess I can blame Gateway. On a brighter note, between doing this, changing HDs, adding fans, cable management, removing unused hardware, and changing GPX card, I now have the confidence to also change out my MB/Processor when the new lineup comes out next year. So I gained some basic computer upgrading skills/understanding , and hopefully I never have to deal with pre-built PCs again.
One big piece of advice I'd really recommend though if it's an available option to you, and that would be to practice on an old PC. It'll familiarize you the general process, and more importantly build your confidence/knowledge.
That being said, you do run the off chance of making a mistake, good luck.