If you mean the very recent batch of changes,
here is a list.If you mean
all changes that have been made from the original games... it would be a bit more work to list those
From memory, the most important changes are:
* Some levels are cropped at the sides, in some cases removing decorative terrain;
* Some levels are adapted to instant bombers (e.g. Fun 6 is called "A task for bombers" and has no blockers);
* Frost 12 and some Genesis levels are adapted to deadly ceilings;
* Some levels have left-facing hatches;
* Dirt style levels with decorative moss over steel have had the moss removed (this is the most recent change).