When you have coins that you want for some reason to exchange for others or just sell them - use the "Convert" tab: 
 

Convert amounts

To convert one coin to another it is required:

1. Select the coin you are giving away;
2. Specify the coin you want to receive;
3. Specify the amount of the coin you want to give or the amount you want to receive;
4. The service will automatically calculate the amount on the other side of the transaction;
5. Press "Send" to send the convert transaction.

And here it is important to understand that the price of any coin changes with each exchange transaction (buy or sell). After you have specified the amounts to be exchanged, but before you have not clicked "Send", other transactions from other users may take place in the blockchain. Depending on the type of transactions, the volume of transactions before your transaction and the parameters of the coins (their pricing), the price during your transaction may not correspond to the pre-calculated values. The transaction before your transaction can significantly change the price parameter of the coins to be exchanged. Therefore, the service indicates that the calculated price is approximate.

This is the specifics of the Decimal blockchian and the pricing model of custom coins in its network. Be careful!