Improving insulation for upstairs bedroom in cape

Hello,

I recently bought my first house... it's a cape built in 1953 and located in Connecticut. One of the upstairs bedrooms has ceiling tiles which I plan to replace with drywall. The ceiling is vaulted with the sides at a 45 degree slope and the top is flat. I removed a few of the panels on the sloped part and saw there is a layer of rock wool insulation about 2.5 inches thick. It's the only thing between the roof of my house and the bedroom ceiling. The rock wool extends down to the knee walls where a previous owner covered it with cardboard (maybe to hold it up?). I did not see any baffles under the insulation to allow air movement. The house doesn't have soffits so I don't think I have any venting in this part of ceiling or knee walls. I believe the only venting is at the top above the flat part of the ceiling. There is a ridge at the top of the roof along with gable vents on each side of the house.

As with many older cape's, the temperature upstairs is always colder in the winter and hotter in the summer compared to the rest of the house. I'm not very knowledgable about insulation. Is what I have adequate or should I replace with a newer material? The insulation was made by Gold Bond and there is paper backing on both sides which I believe is a vapor barrier. The R value wasn't listed on the material. The ceiling will be down so if I should update the insulation this is the time!

Here's a picture of the bedroom ceiling:


Here's a picture where I removed a few of the tiles:


I appreciate any advice! I'm a newbie looking to learn!

Thanks!
Mark