Assuming you mean the entire resort:
Transportation
For Starters I'd have my entrance for parking be upgraded.
Moving onto the parking garages, if possible upgrade those as well or re-build at least one wit updated technology. They work now sure,Universal is becoming bigger and will need to be more accessed.Keep things up to date just for kicks.
Change the parking signage to current resort representations. (Removing Jaws from the parking)
Update resort signage. More led lights and colors so people know where they are going.
Improve transportation drop off so vehicles do not have to back up.
City Walk
Renovate AMC. My favorite of course but, Not as nice as Disney Springs, sorry. Maybe even add a forks and screens.
Add a Universal/FunZone. Something Disney Quest like but with the Dreamworks/Illumination Characters .
Add bowling or lazer tag/escape room. Much like the mini gold, it can be well themed.
Waterfront restaurant. Either fine dining or casual with a performance stage/dance floor.
Implement a kids area. Much of the parks is already anti-children (Just joking) but having something where parents don't have to pay would be amazing in city walk with all the colors, noises, and action.
Add more seating areas and benches.
USF
Remove Mummy Ride and replace it with new Men In Black Shooter/Arcade ride.
Retheme Rockit.
Move entire Menion Mayhem ride to Men In Black area and give it a mini land next to Springfield
Menion and Shreck area gets re-worked to be your new Universal-Through-Out-The-Years attraction featuring Universal Original content and new content from today. (Think GMR)
Add more Waterfront eating/restaurant. They should take advantage of it it's beautiful.
Add a water attraction. I loveIOA but hate going there just to get wet and cool off then come back.
Rid of Animal Actors, ET, and all that follows that colorful path behind for Nintendo.
Find a way to make the Hogwarts Express Entrance/Exit go into Diagon (Unless it's not supposed too?)
Add ride attraction to Diagon. One ride attraction is abysmal for such a grand themed area.
Rid of Hollywood theme, completely re-do entrance and front of park.
IOA
(Dont Kill Me) Remove entire Marvel presence and replace with something they actually own.
Remove entire lost continent.
Remove entire toon lagoon.
Remove Dragon Challenge/Flying Unicorn and re-work Hogwarts express to drop of in front of Hogwarts (Unless it's supposed to be the way it is, I do not actually know but the drop of locations do seem odd for something called Hogwarts express).
Lakefront restaurant replacement of Mythos (Dont kill me )
Add Jurassic Park attraction.
Remove or rebuild/update Jurassic Park Discovery center/restaurant.
Add Suess attraction or characters to be in suess land, more suess trees, houses, it's just bare.
Re-Work Jurassic Park pathway from toon Lagoon (removing Popeye)
Conclusion
But I actually like Universal Orlando the way it is as a visitor. I do hope they continue to improve and provide top line attractions.