Actually, it can be simpler than that.
Just copy your *.ftm files and associated ftm media folders to your external hard drive or thumbnail drive, or directly if you have a cable to connect the two computers directly to each other. Then copy the files to your new hard drive.
In FTM, go to File > Open and browse to the *.ftm file you want to open.
There is no need to go through the backup routine.
The impression left in the prior message that the *.ftmb file is compressed is not true. The backup file is not compressed and takes as much space as the old ftm file plus images take.