Rinsing most of the old sand to remove the crud and detritus is good. Getting new sand is not necessary.
Save and don't rinse a gallon or so of the old sand so that the bugs and worms in it can repopulate the sand bed.
I just moved a tank yesterday. It was an upgrade from a stand alone 40 to a 75 with a 20 gal sump/Refugium. We used all the old sand as above, but first added a 1" layer of the extraordinary Utah Oolitic Sand on the bottom. Utah sand makes an awesome lower sand bed because it has more surface area for a larger population of bacteria. Bacteria is the workhorse of the bio-filtration.
Aloha