AVHD is a file created when you perform snapshot. Once you delete the snapshot and shutdown the Virtual Machine, automatically AVHD will merge with VHD but....
Dunno how , something cause the the merging did not happen. Well, it just happen to me whereby i had VHD and AVHD file even snapshot is deleted and Virtual Machine has shutdown.
Then the question is how to merge AVHD to parent VHD to become one file.
Here is what you should do:
1. Go to Actions and click Edit Disk

2. Select AVHD file

3. Select Merge option

4. Select merge to the parent virtual hard disk.

5.Review the settings and click Finish

Gosh ! Never expect merge options available in Edit Disk options...