I did the same thing pretty much about a month back, upgrading from a 40 l to 120. Here's what I did:
Emptied all but about 1.5 inches of water from old tank into buckets.
Netted my fish (3 platys, 4 corys and 6 danios) and transferred to one of the buckets of old tank water.
Moved the old tank onto another surface and put the new one in its place.
Put substrate, some new dechlorinated water and decor into the new tank.
Put back all the old tank water, transferred the fish back and topped up with more dechlorinated water.
I was using a new, bigger filter so for the first week or so I added used media from the old filter to the new filter, I also added Evolutiion Aqua's Pure Aquarium to kick start the bacteria in the new filter.
I was quite nervous about the whole thing before I started but everything fell into place. A month on and the new tank is doing well, water quality stable and I have just added 3 pearl gourami and a bristlenose plec.
Good luck, I hope it all goes well!