Disconnect the battery cables?

Its' a good idea to do that and if available have it eh battery charged at least once a month. Or get an automatic battery charger that shuts itself off when it's charged.

MUST be dual cable for POS one goes to starter and other to fues box. Why are you replacing?

You have the wrong cables or universal cables. For the black negative cable, the fat one bolts to the engine and the smaller one bolts to the body. If your new cable doesn't have the small one built in, just add a wire from anywhere on the engine to the body. That is needed for the ground return path for lights, radio, heater fan, and stuff like that.

The fat red positive cable goes to the starter motor, but very often there will be a second one going to the under-hood fuse box. If you need that second cable and it's not in your replacement, the easiest thing to do is buy or make one that bolts to the battery cable clamp on one end and to the fuse box on the other. Tighten the cable clamp first, then add the second wire and a second nut to the clamp's bolt. You can attach the black negative one that way too. In fact, you might consider just cutting the old smaller black wire off the cable clamp and attaching it right to the new cable clamp. Don't just wrap the strands of wire around the bolt though. Crimp and solder a terminal "eye" onto it.