Hi I am unsure how to dress baby when it is warmer at bed time and then cool from midnight or early am, especially when they sleep through the night and therefore doesn't get into a change of clothing. Some say baby should wear enough for the coldest time of the night. However, that would be too warm for when baby goes to bed. Therefore, I am confused on what to do. Eg. 25 degrees in the room around 7pm bedtime, and 19 degrees after 2 am.

Bedding amount can often be difficult to determine, but Red Nose does have a few suggestions/recommendations.
Have a read of these:
https://rednose.org.au/article/bedding-amount-recommended-for-safe-sleep
https://rednose.org.au/article/how-much-bedding-does-baby-need

Key recommendations are to ensure baby’s head & face remain uncovered.
If your baby is active & rolling, often kicking off any blankets, it may be preferable to use a sleeping bag, where an extra layer of clothing can be added as required to keep baby warm.
6 degree change in temperature is not large.
Important not to overdress.
Is your baby waking unusually, in the early hours of the morning?