Take all creatures and LR out as you stated and place them in the 10gal or larger if they won't fit comfortagbly in the smaller tank for a few weeks.
Depending on how long you have been running your UGF would make the difference on how polluted your existing water is. If your nitrates are off the test kit scale, then I'd suggest using very little, no no water from the existing setup. Break the whole thing down and start anew from the beginning. If it is relatively new, and your nitrates are ok, then use the existing water.
Get rid of the wet-dry as it is a nitrate factory as is the ugf.
LS with DSB of at least 5". Return the LR to your tank, once the "dust" settles when you add the sand. I don't know how much LR you have?
Let the tank cycle. You can enhance the cycle of your new tank by using dead shrimp to facilitatie the cycle and increase bio-load capacity. If you have zero readings on ammonia and nitrite, then add 1 fish back at a time---take it very slowly, cause you have such a small tank, that the margin for error is significant. You can enhance the cycle of your new tank using dead shrimp.
Use good PH circulation [probably at least 2 for your tank].
Get rid of cc, ugf, and w/d
Have a good time!