Chevy & GMC Vans

Had to use cheap coolant one day because I couldn't get the Dex cool. Now I want to replace the coolant with the good stuff. How do I go about doing this myself? Please help.

open the petcock, drain & refill. If you want to flush the entire system, disconnect each hose at both ends, insert the garden hose and flush til clear. reconnect and refill.

Last time I drained cooling system, I used the block drain bolt.