Good timing, I just did this yesterday.
I transfered 16 fish and 2 frogs from my old 20g to my new, super deluxe 46g bowfront.
I got the 46g to 7.0 ph, the 20g was a little low at 6.8.
Temp was within 4 degrees.
I put some Aqua-safe in the 46g to help with the stress. Bio-coat works well too.
1. I got a large bowl and put about 16 ounces of water from each tank in it.
2. Then I got 3 to 4 fish, let them sit in the bowl for about 15 minutes, then put them in their new home. I like to cover the bowl to keep them from jumping out.
3. Dump the water from the bowl.
Go back to step 1 and repeat till done.
No lost fish, color is great, all very happy.