It will be messy so prepare to mop up. Buy a little hand held steam cleaner, the jet of pressurised steam from the nozzle attachment makes it easy to target thick ice deposits to get the job completed asap. Previously I used bowls of boiled water in the empty freezer to speed things up. Careful when knocking ice off the internal pipes, they can crack. Before I moved I had a frost free model... the best, no defrosting needed.
We usually spread a few old towels on the floor and keep a few others handy for mopping up what comes out. Then put a big basin of boiling water in the freezer and use a hairdrier as well to speed up the process!