As far as I know both DOT3 and 4 are compatabe.
the major difference is that DOT4 has a higher boiling point (both wet and dry).
If you ride hard then I would.
If the bike is a little older (maybe 3 years) then you might want take the time to change the lines too. They tend to bulge a little after a while.
It won't ruin the system to use DOT3 but if the brake start to fade or feel spongy under repeated hard braking then switch back to DOT4.
I lent my manual out so a don't know when it calls for brake line replacement.
I'm sure somebody here will look it up for you.
If I'm wrong somebody is sure to correct me.