How do you know if a tire will fit your bike? For instance, my current tires are 26x2.0 but I am looking at a street tire in a 26x2.5 size. How do I know that will fit?
Yeah. Assuming you have a pretty standard mtb rim (not like the Surly Large Marge or anything), you can go up or down in width a little bit with no problem.
Don't sweat it. I couldn't get a new chain on this past weekend and it wasn't even the first time I was replacing it. I EVEN BROKE MY CHAIN TOOL IN THE PROCESS!! I had to let the shop guys do it. Everyone's a beginner with some aspect of bike maintenance.