You're only 13 so take some good advice.
Feel free to screw up because that's how you learn.
Everybody messes up the first time they try something so welcome to the club. Heck.. the first time I changed strings I wound them on backwards and didn't know anything about stretching them out so they constantly went out of tune. But the next time I changed them, I read a couple of books on the subject and did a pretty good job.
Now it's just second nature.

Think of it like part of the process of learning to play guitar.
The only way you're going to get better is to practice and the only way you'll learn to change your own strings is by giving it a shot a few times.