newbie buying new tank.

Her guys, I'm buying a salt water tank and was hoping to get some tips on transporting tank/fish and live stock from existing house to my own :). The tank is 3 year old with fish and live rock. From what I've researched it's a good idea to change the sand. Apart from this I really don't know what I'm doing.. Not sure if it's as simple as grabbing as much existing water as possible. Getting it back to temp... Then throw the fish in??? Any help would be greatly appreciated... Tank comes as full set up so I believe I will have everything needed for my new hobby.. Thank you so much in advance to anyone that can help me in anyway..

Cheers lads and lasses