Ist, by riding more, you will build up strength. Haven't you already noticed that?
A much simpler change is to a different cassette. Maybe a 12-23/26 or a 13-26?
Do you use the small ring?
Look to these links for some of the available cassettes-
http://sheldonbrown.com/harris/k7.html#8
http://aebike.com/page.cfm?PageID=30...ory=556&type=T
Look at this link. It's a gear calculator-(I just use a spreadsheet myself so I can look at various options side by side.
http://sheldonbrown.com/gears/