Johan - I was going to type it all out, but if you go to the links at Perth for the DML Early A and Late A kits, he's got a complete list of the differences all laid out.
http://www.perthmilitarymodelling.com/reviews/vehicles/dragon/dr6160.htm
http://www.perthmilitarymodelling.com/reviews/vehicles/dragon/dr6168.htm
The biggest differences are the type of mount for the hull machine gun (ball vs letterbox), the mantlet (one hole vs two hole), and the presence of the pistol ports on the turret.
If you've got any more questions after reading those links, let me know!