The seven times Formula One champion, who has not won a race since 2021, was third fastest in the first session and sixth in the second.
"I've generally had an amazing day, I really enjoyed driving today," he said.
"I want to say a big, big thank you to everyone back at the factory because to build and design and develop a car is not an easy thing and everyone’s put so much time in, so many hours of hard work to have us here today.
"I’m glad that we were able to keep it on track for them and I think we got a lot of data. It’s not the place to ultimately test an upgrade but the car was generally feeling good."
Hamilton said he could feel the improvements and Mercedes just had to keep "chipping away" to squeeze more performance from the car.
Mercedes are third in the championship but a long way behind champions Red Bull, who have won every race this year and finished one-two in four of the five.
Teammate George Russell agreed that a real analysis of the upgrade would have to wait until after next week's Spanish Grand Prix in Barcelona.
"Monaco’s such a unique circuit it’s not really the place to be evaluating any updates or changes, and we knew that coming into the weekend so we’re almost forgetting about the upgrades," said the Briton.
"We’ll worry about that next weekend and just focus on trying to improve around here.
"There’s definitely some positive signs to take from the (second) session, definitely improved from FP1," added Russell who was 15th and 12th.
