An "album" in Gallery is a folder on the phone. Use your file manager app to move the files from the folder they're in to the folder you want them in.
Be careful. If you have 2 folders, one names sdcard0/DCIM/Camera/Vacation and another one named sdcard0/DCIM/Vacation, you'll have 2 albums named Vacation. The album name only picks up the last folder name. So try not to duplicate folder names in different parts of storage or you'll have a problem figuring out which Vacation folder the picture in one of the Vacation albums is in. (You'll have to go looking for it with the file manager.)