Rollers are one of the more DIY-friendly parts on a garage door, and we won't pretend otherwise - that's the honest limitation on this page. If your door is a single panel, low to the ground, and you're comfortable with a socket wrench and a ladder, replacing a bottom roller yourself isn't unreasonable.
Where it stops being a weekend job is anything above the bottom bracket on a door still running the original 1970s-era spring and track setup. Those brackets carry cable tension, and on a door this age the mounting hardware is often as tired as the roller you're trying to replace. If you're not sure which bracket you're looking at, that's the point to call rather than the point to find out.