Tektro mechanical brakes can be adjusted with a 5 mm allen wrench. There is a screw in the middle of the caliper, tighten it one or two notches to bring handle back to original position.
Inspect the pads from the side, you should see two colors. There should be substantial grey pad left. I get about 2000 miles out of a brake pad on the wheel I am using most. More on the one I don't use much.
When the grey material gets really thin, replace pads. Takes in addition a 10 mm combo wrench to get the caliper the strut, then a thin plier to bend the cotter pin and push it through. If you want to cut the cotter pin they sell new ones at the auto supply, in boxes of 1000.
You don't need to loosen or adjust the cable postion, at least I didn't. If your cables are stretching replace with Clark's or Jaguar. I like the lubricated SS version, but I park my bike out in the rain frequently.