How do you remove a mirrored database SQL Server 2012
The operation cannot be performed on database "test0224aEd62" because it is involved in a database mirroring session or an availability group. 


The error is self explanatory .. you cannot drop a database if it is part of DB mirroring, AlwaysON or replication.

I normally avoid using GUI when I have option of doing same thing using TSQL ...

For future readers, you can break database mirroring using below TSQL command (run it on the secondary server)

ALTER DATABASE &lt;&lt;DB NAME&gt;&gt; SET PARTNER OFF


Once mirroring is broken, then you can drop that database using 

alter database &lt;&lt;db name&gt;&gt; set single_user with rollback immediate
go
drop database &lt;&lt;db name&gt;&gt;
go