Looks pretty corroded. If needed, spray it down with a penetrating oil. Loosen the nut closest to the inside of the window frame. Then work the cube and handle assembly loose. As you pull in on the assembly, you will then be able to remove the nuts and locking bar at the other end. After they are off, continue removing the nut on the inside....until you can remove it as well. You can then remove the entire unit. When you get the new unit, it will take some fussing to get the nuts in the right places to engage the window lock.