It is easy to do in many cases. Take the following two theories:

Rocks falls downwards since masses attracts each other.

Rocks falls downwards due to invisible ghosts making masses attract each other.

Both of these theories have the same amount of evidence supporting them, but one is strictly simpler than the other. If one theory isn't a simple reduction of the other then Occam's razor doesn't apply, but in those cases it is usually possible to make experiments which disproves one of them.

Less is not arbitrary. Be it fewer assumptions, variables, bits, rules... And these are all abstractions. Abstractions can be counted, so all simple really means is fewer abstractions. Theories tend to refine themselves because ultimately we arrive at one word, and with new evidence, even words will adapt. What was gravity yesterday is graviton today.