You can get the latest versions of all software and manuals for your T6i here: Support | DSLR | EOS Rebel T6i | Canon USA
But you do not need any software to download the images from your camera. Just use an SD card reader. Faster and more reliable.
you don't necessarily need special software to load images from your camera to your Mac. If you have an SD card slot then simply take the card out of the camera and plug it in. The software should see it as a drive. If you don't have such a slot, then consider getting an adapter - sometimes the simplest is the most reliable and elegant.