what will happen if theres no more room to grow up for my plant?

i am planting 2 regular plant in a 1x1x1,2 meters growbox
i switched the hps light to 12/12 about a week ago and now the plant has grown like crazy
both plant has reached the top of my growbox and i cant move it up a bit more, what will happen to my plant?
the plant dont seem to die or anything

will it actually make the flowering process faster? now you can actually see that the flowering stage has begun

and btw the plant is around 60-70cm in height

Read up on supercropping and LST.

Try tying it down (LST)

is there a link that you guys can provide me with so that i can read about it? since im quite confused of which part of the plant should i tie down

http://www.mmmfaq.com/stress-training-marijuana/ This is essentially the method I use but I go a little bit more extreme. My plants have never finished more than 2 feet tall. My grow is in my signature. The biggest thing with LST is to start early before the plants become too rigid and experiment. Don't be afraid to try some stuff. Adapt these methods to what suits you. Good Luck and happy growing.

Oh and it will take a few cycles to get everything just how you want it but I continue to LST through the transition phase between veg and flower to maintain the canopy. After that, I just let them go. If something gets too tall, I pull it down a little so it doesn't shade anything. My best results have come from maintaining a relatively even canopy and getting rid of all the growth under the canopy that doesn't get light. I also get rid of any fan leaves that block growth shoots from getting light during transition, and anything that will cover the top parts of my buds goes as well. This method requires a little more attention but as far as I am concerned, I could stay in their all day anyway.

supercropping works great and gives you more branches and more branches give you more buds.......

okay i just bought some wool strings and will try to tie it down as much as i can lets see how can i do
thanks for the help guys, can i actually bend the top part of the plant? or just the sides?

You can tie down the top with no prob.