I heard there is a bus that will transfer you between terminals so you wont be leaving the airport. Alternatively, if you have a British passport, or one that doesn't require a visa, then you should be free to leave the airport at terminal 3 and go to terminal 2.
You can try calling Dnata, the should be able to tell you for sure.
Question......
When your changing terminals do you need a transit visa? For example going from terminal 3 to terminal 2? Technically your not entering UAE but I do know that terminal 2 is a bit far out from terminal 3 and not sure how that works.