How can I convert altcoin to Bitcoin?

Go to bittrex, deposit your BTC into the wallet, then trade for altcoins on the main market screen.

How can I convert altcoin to Bitcoin?

Go to bittrex, deposit your BTC into the wallet, then trade for altcoins on the main market screen.

I mean altcoin to Bitcoin

Same way? Deposit your altcoin on an exchange, assuming its on the exchange you will be able to trade it for BTC.