ok if you're just keeping the new tank running it's straight forward
fill the new tank with dechlorinated water, set up the heater so it comes up to temp
add your substrate, decor, plants etc
turn off the filter on the old tank, take the media from it and put it into the new tanks filter
hook up the filter on the new tank and turn it on
check the temp of the new tank, if it's at the right range then you're ready to move the fish
remove all decor from the old tank, drain water until there's just enough to cover the fish
get 2 nets, use one net to chase the fish into the other net, when caught transfer them as quickly and steadily as possible to the new tank
when all the fish are caught and moved then turn the light on the new tank off, resist the urge to feed the fish or mess with the tank, just leave it alone for 24hrs unless you see something desperatley untoward (i.e. fish dying)
drain the rest of the water from the old tank, tidy it all away
next day check the levels on the new tank, if there's any ammonia or nitrite (shoudln't be if you follow above instructions but you never know) then do a large water change