If my erc20 tokens gets a value, How can i convert my erc20 token to ETH?
You can use etherdelta.com to convert your token to ETH. All you need to do is to import your wallet in ether delta. Before you do it, make sure to keep your private key safe and don't share it to other. Etherdelta may need your private key to import your account to them. That's what I do to convert my token to ETH.
You can do that and trade with IDEX also. Please use metamask as possible as it is safe and easy to use. You only put and store your private keys in metamask and you will not do it in metamask again, less exposure of your private keys when you trade.