yeah, you should be able to just tighten them up. should be an allen key bolt up top and a nut underneath (just the one, poor fella).
if you find it keeps working itself loose, get some 'nylock' nuts instead. they've basically got a plastic insert that does a much better job of keeping it all together.
if in doubt ask your local bike shop, they'll know what you're on about.
oh yeah, don't overtighten - make sure your levers still move freely, in the direction they're supposed to...