Originally Posted by Oneder

There is a bottom bracket tool, what one depends on what your bottom bracket is. You will take it off and see what's in there. Probably cup and cone bearings but they might be in a race. Probably 1/4 inch but possibly slightly smaller. Just take them out and see what you have, then get new bearings of the right size they are cheap. Grease them up and put everything back together. If you can't find the right tool you can use a hammer and chisel to unscrew it.