you can tie them down and let them start growing outwards or you can just move them to a larger space. Honestly.. I had 10 that outgrew a 4x4x7 closet and I just moved them into a walk in closet and they kept growing and budding even above the reflector...
you should be fine... the bigger they are is the more bud sites you will see in the end
i would do some low stress training... take the top and tie it down (gently) to hold it horizontally... this will reduce the height of the plant, and give more light to the bottom branches to make more bud
if it gets really too cramped, you could go to casa dePOT and get a screen, its in the fencing area - get a plastic one with about 2" x 2" square holes in it... tie that over the top of your plant and do a SCROG (screen of green) - pull the buds through it and the buds will prob grow 6-8" over the top of the screen... check out my photo gallery for some pics on how to scrog.