Trying to build a lighter body....

I'm a 45yo. Male who has been banging heavy weights and running/biking for years. I'm currently 6'0 205lbs, and I've been this weight forever. I never seem to gain or lose a single pound year-to-year. I'd like to be a little lighter on my feet -- say between 190-195lbs. Can anyone reccomend to me how to change my training? I've been told heavy weights will lead you to a heavier body. Occassionally, I'll take a week off without exercising and my body feels great. I actually feel lighter too during the week I take off. Can anyone give me suggestions?

Thanks.

Ryno