I'm just going to list the differences for each class.
1st Class:
1. The Grand Staircase & Aft Grand Staircase was painted an avocado green and fitted with handrails
2. The R&WR remained the same but the alcove was removed
3. A dance-floor and a movable cinema screen was fitted to the 1st class Lounge
4. The smoke room remained the same, I believe
5. The Verandah and Palm Court remained the same, I believe (couldn't find anything about this)
6. The Restaurant was extended on the port side
7. Parisien Cafe it was modernized with darker tones to match the Restaurant
8. A Ladies hairdresser salon was added to the C Deck landing of the Aft Staircase
9. The Reception Room was made larger but otherwise remained the same.
10. A dance-floor was added to the middle of the Dining saloon and the room was rearranged
11. The gymnasium, Squash court, swimming bath, Turkish Bath remained the same
12. Some E Deck 1st Class cabins were converted to Tourist Class
2nd Class:
1. the 2nd Class Dining Saloon was split and the port side was given to Tourist Class
2. 2nd Class Library was converted to R&WR and a dance-floor was added at some point
3. 2nd Class Smoke Room may have been remained the same
3rd Class:
1. the 3rd Class Dining Saloon remained the same, I believe
2. The Crew quarters in the bow were removed and given to 3rd Class
3. The 3rd Class cabins in the stern were given to the Tourist Class
4. The 3rd Class Stairwell in the stern was given to the Tourist Class
5. The 3rd Class Lounge/General Room was given to the Tourist Class
6. The 3rd Class Smoke Room was given to the Tourist Class
7. The Open Space was split up into a 3rd Class Smoke Room and Lounge
