I just did mine after having the stock exhaust on for over 18K miles. Soak the clamp bolts/nuts with some kind of penetrating lubricant. Let it sit for a few minutes. Air tools really make the job easier if available. Hand tools are going to take you forever. Anyhow, after the clamps are loose, spray lubricant where the pipes slip together. Start at the back of the truck and remove the tips first. Spray the rubber hangers with lubricant too in order to slip them off. Just keep wiggling and working the slip joints loose while pulling towards the back of the truck. It's slow going but they really do come apart.
Installation of the Magnaflow is just the opposite procedure. You can lube it's slip joints in order to make slipping them together a little easier. Put the clamps around the pipes before you push them together. Just keep working it back and forth while your pushing on it until you reach it's limits. Then tighten up the clamps.Then enjoy the new sound.