I have a century coming up that I am less than prepared for. I know I can sit on my bike for 100 miles but I haven't trained hills much at all. I've been going to spinning class and doing weights, however, so I'm not completely lost but still...

I am on an Orbea with Campy Veloce. It's a compact double with 50/34 in the front and 12-25 in the back. Is it possible to change the rear cassette to include a few larger gears? I think the rear would be easier to change than the front but would any of this require major work?

The alternative is to walk when I need to and exercise a lot more. I'm just looking for a quick and easy fix for the next couple of months! I'll ask my LBS but thought I'd throw it out here because there are so many knowledgeable people here.

Thanks! Yes, it's a pathetic stab at salvaging something, I'm not sure what.