Its possible but would be costly. You'd need shifters, casette, possibly new wheels if your hubs can't do 10 speed casette, rear derailleur (FD would be okay I think). I have left my 9 speed bikes as is because I just don't think I would glean much additional benefit for the expense of adding one cog in the back. I'll woprry about when i can no longer get replacement parts for the 9 speed.