Removing an encrypted disk image

A while ago, I created a 7gb encrypted read/write disk image and put some files in it. Now, recently, I removed the files in the encrypted disk image and copied them back into the regular HD. I erased the mounted disk image and now says it's back to 7gb.

How do I remove the disk image? It's still there in my documents folder. How do I melt it back into the HD space? I can remove it from the side bar on the disk utility page but it's still on my HD and I can still mount it to the finder. I enter my password and it mounts.

I want to get rid of that disk partition as I don't use it anymore. What do I do? Is it there forever and am I stuck with it?

Thanks in advance for anybody that can help me with this.