Chose a heavy with a motar and then go after them.
Also a scout is faster than the turret and if you can ski. (hit jump as you move down a hill then at the bottom hit jet pack, will send you way up or way out.) Look to
www.tribalwar.com or
www.planettribes.com for tips and pointers.
Also the bLaster at close range will take out a turret, but you have to be right up on it.