I will be swapping my cassette from one wheel to another. I am doing a SRAM/shimano compatible cassette and hubs.
grab your wheel which currently has the cassette.
slink your chain whip around your cassette. you will be turning the wrench left, so put your chain whip on in a manor to hold it steady from the right.
put your adapter in your wrench. slide the adapter in to the lock ring. (the thing on the end of the cassette with the matching grooves). note, not all lock ring brands use the same adapter type.
after you initially loosen with your wrench. spin the lock ring off with your fingers.
pull the cogs off the hub. they will slide right off.
start putting the cogs back in, largest first. there are grooves on the hub that will match up with the cog grooves. keep track of which cogs have spacers and make sure to put the spacers in.
all the cogs are on! ps. take out your skewer, I forgot too. it is the quick release axel for those who don't know.
grease the threads on your lock ring before reinstalling it.
tighten the lock ring down by hand using your adapter.
finish tightening with your wrench.
PRESTO! you did it!
put your wheels back on and go for a ride!