Decrypt of virtual drive after 10.3 installation

I have an encrypted virtual disk set up using 10.2.  It is running out of space and so I want to decrypt it, create a new larger disk and then re-encrypt both using 10.3 which I installed recently.  When I go to the tools to decrypt, the decrypt command is greyed out and so I don't seem to be able to decrypt it.

Please can someone tell me:

1.  If I create a new encrypted disk and copy the files from the old to the new can I then delete the old disk without decrypting it?

2.  Why can I not decrypt the original disk using 10.3.

I have all the appropriate pasphrases etc.

Many thanks