This will be helpful to newbies.
You cannot convert your tokens into ethreum using myetherwallet as myetherwallet is an exchange platforms. If you find out that the tokens that you want to convert is listed in any exchange of both decentralized and centralized one you will need to transfer the token to those exchange and covert by selling them for Ethereum there.
You just have to transfer it to any exchange where it was listed then you can sell them or but new tokens that you like, then transfer it again to desire wallet to in cash it..
YouTube has the instruction how to transfer your token from Mew since its a little bit tricky..
This is what he need to do. I also asked this question here before and I don't even know that the simple thing is to see your tokens as coins which need to be buy by another person and not conventions.