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I assume you are talking about a brake on an AR? If your barrel is threaded all you need is a 7/8 wrench or an armorer's tool. A vice and vice block is handy but not required.
Clear weapon and varify the chamber is empty.
Remove upper from lower and remove bolt. (Just for safety)
Remove the current muzzle device. (Counter clockwise)
Clean the threads and remove any loctite that may be on the threads.
Apply new loctite if desired. ( I don't loctite mine but do apply copper anti-seize)
Thread on new muzzle device and torque to manufacturer's spec.