Tge 1.5

Well, i've been away from programming for a bit. I purchased TGE 1.4 a while ago and came back to GG to look at the new updates to the engine as i'm getting a little more time to program. I'm still a newb at game programming and am buying 3D Game Programming All in One to guide me through it. I have noticed that 1.5 comes with a lot of improvements. The question I have is... can i download 1.5 or do I have to buy the update? If so, is there a discount since it's $150 and i got 1.4 for $100.....