If you spend a certain amount of coins, you can exchange fragments of heroes of low quality for fragments of more powerful characters. If you are not satisfied with the current exchange formula you can change it for copper coins. At 24:00 Moscow time the exchange will reset automatically. Please mind that the number of exchanges is limited.
In this interface you can exchange one of your artifacts to one of the four others. The number of options can be reduced by clicking the "Throw" button under one of the artifacts, but this feature will require an additional amount of coins.