After a DVT what are your INR levels suppose to be at in order to be able to come off the warfarin?

Not related. The inr is not used to come off the warfarin. Inr is a measure of the blood clotting ability and is used to monitor the effect of the warfarin. The goal is between 2 and 3. If less than 2, the warfarin effect is not enough to protect one and > 3 it causes excess bleeding risk. The duration of therapy depends on circumstances surrounding the DVT and can range from 3 months to lifetime treatment.
Time not level. As dr. Depietro said, keeping your INR beteen 2 and 3 while you take Coumadin (warfarin) is important but how long you stay on Coumadin (warfarin) depends on a number of factors that aren't determined by your inr.