I have three principles for changing earlier pages:
1) The law of doubling. If your old art is a 4 and you're now an 8, go ahead and revamp.
2) If you see a narrative flaw where inserting a few panels will improve the storytelling.
3) You completely change your style.
The above said, only do it if you can still create new pages on time or your old pages are driving you to madness.
In your particular case, in terms of style, your old pages are similar to the newer ones. I'd keep on going and not stress about the early pages. You'll keep growing.