Things You'll Need
Instructions
 
Pull off the legs and head pieces from the LEGO figure. 
Attach a 2-by-2 brick to the top of the legs. 
Attach a 2-by-4 brick on top of the 2-by-2 brick, and two 2-by-6 bricks evenly on top of that. 
Add two 2-by-3 bricks to the sides of the 2-by-6 brick so that they cover one section on both ends and leave a 2-by-2 portion hanging over the sides. This will leave a 2-by-4 section in the middle which must be filled by a 2-by-4 brick. 
Attach two 2-by-4 bricks on either side of this section so that a 2-by-2 portion is left in the middle. Attach the head here, and place it in the middle of the four notches so that it is secure. 
Attach the two 2-by-8 bricks under the overhanging 2-by-3 bricks so that they stick outward like arms. 
Attach under both arm bricks a 2-by-4 brick in the middle to provide girth. Attach a 2-by-2 brick under the remaining space on the front of the arms so two notches are attached to give the LEGO Tank fists.