I know you're supposed to notify other agents if you get an offer from an agent, but not to notify them if you get a full request. But what if you get a Revise and Resubmit? Should you let others with the full know? How are you supposed to know whether to proceed with the request if others still have the full? Should you give them a head's up?
Don't assume that the requested revisions improve the book. Just cause An Agent said it, doesn't make it the best choice.
It's one thing to say the pacing is off in the middle chunk of the book; it's another thing entirely to say all your characters need to be vegan cause that's the new hot thing in dino porn, and oh by the way more sex scenes so it's not Lickosaurus lite.
However, if you do decide to undertake major revisions, what you can do is withdraw your manuscript from the other agents who have it, revise, then send it back.
Most of us would rather read the version you think is best.
You don't HAVE to do that; you CAN do it.
You can also let the submissions run their course. I can hear you muttering on your hamster wheel "but what if this new revision would have worked where the first version didn't??!!??"
And that is why writer should always have bottle of hooch next to their desk.
How to decide?
Well, if the revision requests are things like "pick up the pacing", "develop the characters", "build the world" generally those are things most agents will agree on as problems.
You'd be well advised to withdraw the manuscript, fix the problems and resubmit.
Things that are more idiosyncratic, and more personal reading taste "I didn't like Felix Buttonweezer very much" vary from agent to agent and "fixing" that "problem" might not improve the ms from another agent's point of view.
If those are the revisions requested, you can make them but NOT withdraw the other manuscripts from consideration, and send this revision only to the agent who suggested it.
There is no one right way here.
How to figure out what to do: email the agents with the requested fulls and ask them.
I get these kind of emails and my standard response is "I always want to read your best work. If you intend to revise in a major way, I'd rather read the revisions."
Not all agents will respond that way, but at least you'll know the lay of the land.
Bottom line: you do not have to notify other agents of a revise and resubmit.