I had this exact same problem. It's a tough habit to break, but it all comes down to consciously forcing all your weight into your heels when ever you go up. You have to think, "Up, force heels down...Down, heels relax a little
...Up, weight in heels..." Soon it will become automatic and you won't even have to think about it.
You'll find that doing this will force you to use your leg muscles a lot more. It hurts really bad for the first week or so. Try some stirrup-less to get those legs in shape.