This isn't always true. You have full control over the inputs of an unconfirmed transaction only if the transaction has been marked as RBF.
If your transaction hasn't been marked as RBF, it's very unlikely that you succeed in replacing that with a new transaction spending same input(s). Nodes will reject your transaction
Nodes usually reject any transaction spending UTXOs that have already been spent in a non-RBF transaction, even if the original transaction is still unconfirmed and you have paid a very higher fee for the new transaction.