what are the steps for me to change my thermostat in my 70 chevelle big block. thanks.

OK I'll bite.
Drain the radiator a bit, lower than the t-stat housing.
U-bolt the t-stat housing, No need to remove upper hose.
remove old stat,
scrape old gasket off.
apply some gasket sealer onto new gasket
install new stat,
reinstall and tighten t-stat bolts

add water and check for leaks at operating temp.

drain the radiator.
take the old one out- scrape andy gasket material off the housing and intake manifold..
put the new one in with new gasket.
bolt housing back down.
refill radiator.