If I was going to do that I would:
1st move the LR
2nd remove the fish, coral, invert,ect from the 25 and put them either in a spare bucket or bag.
3 move the sand *that way if you hit a nitro. pocket the fish are safe*
_plus if you have any fish that burrous (ie engineer) the lr is on the glass and not the sand_
(assuming you already have premixed water w/ the same salinity and ph as the 25g)
4 adjust temp of the water accordingly
5 temp aclimate fish/coral/invert/ ect
6 release
I would prob use as much equipment from the 25g as possible on the 55g (filters, powerhead) just so you can keep as much BB as poss. you can always take out once things stabilize. I wouldnt use "old" tank water in the new 55g. Lighting shouldnt be an issue doing what you are planning