Alter database from Read-Only to Regular mode? A warm-standby database is read-only (Error 5063)

I am trying to change the mode of database from "Standby / Read-Only" to "Normal" mode so that I could use mdf file to attach to other SQL Server. One instruction that I got was go to Properties --> Options --> State --> change the Database Read-Only from True to False. Then I got this error message: **A warm-standby database is read-only.** Why do I get this error message and what should I do to change the mode?