whoa! hold on. you don't necessarily need new boots.
where exactly are they loose? can you tell? is it side-to-side width just around the ankle bones? is it everywhere around the heel? maybe it's just around the Achilles tendon?
My Salomon Course X-Scream boots fit too snug at first, just right after a few days, and then after two seasons loosened up to where I had to do some snugging -- but only in the little rectangular "pocket"-shaped sections adjacent to the Achilles on each side. I like to ski in super-thin socks, so any "looseness" in my fit wasn't fixed with a slightly thicker sock. I added some padding to the liner boot and all was well again.
what was the event that made you realize the heel is "too loose"?
if you describe it in detail, we have a better idea of what's going on. without seeing your fit first-hand, it's awfully hard to give any recommendations.