Bending aluminum tubing requires some special tools and is not as simple as many people think. Simply attempting to bend the tubing without the correct method and tools will cause the walls of the tubing to crimp, making the tubing unusable.
You should first determine the extent of the bend that you need and draw it on plywood or similar material to get an accurate plan. Using a jigsaw, you can then cut out the plan to be used as a guide. Clamp this pattern onto a secure and level surface. Tie a heavy line to the end of a spring, inserting this spring into the tubing. The spring should fit fairly as snugly into the tubing as possible so it will need to be about the same diameter.
Secure one end of the tubing in place at one end of the pattern that you have cut out. Pulling the string, you can then bend the tubing in a single, steady movement using the pattern that you cut out as a guideline. It is important not to bend the tubing back and forth, stopping and starting in the process as this will weaken the pipe. Instead, try to bend the tubing in a single movement.