I have upgraded tanks more times than I care to admit. Here was the process the last several times:
1) drain 50-60% of the water
2) drag the tank and stand away from the wall
3) unplug everything
4) put the new tank and stand in place (obviously you can skip that stuff if it's in a different location)
5) now that you aren't in danger of dropping a heavy tank and breaking glass and/or limbs, begin drinking beer
6) drain more water into a big rubbermaid bin (40L I believe)
7) set up air pump and heater in there
8) put fish in there
9) drain the rest of the water into the tub
10) while draining, open another beer
11) use a plastic dustpan to scoop out the sand/gravel into a bucket
12) dump substrate into new tank
13) fill new tank as quickly as possible to a level that'll let the filters fire back up
14) fire the filters up and get them running
15) more beer
16) arrange all your power strips and wiring underneath while it keeps filling
17) make sure the temp is OK and add water conditioner, salt, etc
18) express shock over the fact that none of this was especially difficult, yet somehow it took all night and you are sweating like a one legged fat guy in an ass kicking contest
19) drink more beer
20) put the fish in the new tank
21) put what's left of their original water in with them
22) Cover the new tank
23) move the original tank out to the garage without any help because your girlfriend fell asleep hours ago
23) have another beer, which you have really earned this time because carrying a 75g glass tank and then the stand by yourself is really quite difficult
24) add any new filters you got to handle the increased size of the tank
25) watch and enjoy the fish, taking care to monitor the water params, make sure the filters aren't leaking, etc.
26) take a shower. You don't want your sheets to stink like a day of hard labor.