We have in-app exchange service, which you may use in order to top up your wallet, using other cryptocurrency coins that you have. For example, if you want to top up your BTG wallet using your altcoins, you need to launch your BTG application, go to Exchange option, choose to top up using the altcoin, you may choose it either by the ticker or the title. Then you will see the address where you need to send your altcoins in order to receive BTG coins in your wallet. Pay attention to the minimum amount for exchange. Then you go to your altcoin wallet or stock exchange and make a transaction using this address, after some time you will receive BTG coins to your BTG wallet.