ReUse Rewritable media

The Backup Exec sad me 'Low disk space'.

I saw the media-s, and I found a lot of rewritable media on 'full' disk.

My Question:

Why Backup Exec not reuse rewritable media?

How can I change Media to rewriteble?

How can I delete Media with stored (retired) data? Because if I delete data manualy, then BE not refresh inventory.

Thanks for help

Gyula