If your using a wallet that has utxos management, you would go into the utxo menu, select all the utxos you would want to send (up until the size you chose), and then send it to an address (either in the same wallet or in an another one). Make sure the new address wasn't used before. Once you send, all the utxos you chose would be destroyed and a new utxo would be created. It would have the size of all the ones you chose (minus the fees or not, depending on the wallet settings)