The full verse in Romans 12 says:
Do not conform to the pattern of this world, but be transformed by the renewing of your mind. Then you will be able to test and approve what God’s will is–his good, pleasing and perfect will.
What does your mind do? It absorbs and remembers information, which may be either true or false, and it thinks. Thinking is the crucial part, since much of the remembered information may be false. Only thinking can sort the good from the garbage.
Hence to renew your mind means to rethink. That’s what this site is about. If you count yourself a Christian but your thinking has barely changed, you probably need to rethink. If you are not a Christian, you certainly need to rethink your view of what Christianity really is. It is something far different to a Song and a Sermon on Sunday.