What sort of subjects do you enjoy shooting?
A T5 would be a downgrade.
A T5i would be a very very slight upgrade. The sensor is largely the same, but the T5i has a slightly improved focus system and the articulated LCD is a capacitive touch screen. Don't look for much to change in the image quality department.
A T6i or T6s is a more significant general-purpose upgrade. It has a new sensor, higher resolution, and the "s" version has a second control dial on the back (a bit more like the mid-range and high end models.)
A 70D, 7D II, or 6D would be a more noticeable upgrade. But which of these offers the most improvement really depends on what sort of subjects you like to shoot. The 6D will have the best low light performance. The 7D II will have the best fast action performance and the best focus system. The 70D has a little of everything... a better focus system (but not nearly as good as the 7D II, but better than the 6D), better video capability, and fairly quick shooting speed (but not as fast as the original 7D nor the 7D II.) The 70D is the most affordable of the three.
I should not neglect to mention... often you'll get a much more noticeable improvement by upgrading lighting and lenses than you will get out of upgrading the body. Which lenses are you using and what are you shooting with them?