I am facing the same problem, top tip would be get better props and a grass feild, the problem is with the tuning... Have u set min and max throttle setting on your esc?
Here is a small check list as to what u should do when u build a quad:
1. Make sure each ESC is collaborated with the min and max throttle
2. make sure u take it off in attitude mode without any other settings like a to +
3. Make sure all other sticks except throttle is at dead centre
4. Make sure you have a soft ground which will not cause damage to anything (grass feilds are the best to test the as your props would survive the crash)
5. Be ready for a crash anytime and always carry more props than what you need
6. Make sure that you remove props when you hook the quad up to the computer
7. Start with PID settings of someone else who is having a "stable" flight(if you don't know what pids are it would be understandable as to why you're having such a difficult time with the unstablility of the 250 quad) don't break your head around PID settings just yet
learn how to fly and then we will talk about pids