Tools > Preferences > Fees > Enable Replace-by-Fee. And tick "Replaceable" when you're sending.
The transactions you sent this way will be marked as replaceable, you can increase the fee by right-clicking and choose "Increase fee". You can mark a transaction as final when increasing the fee, doing this will make you unable to increase the fee again (after you broadcasted the "final" transaction).
The transactions you sent this way will be marked as replaceable, you can increase the fee by right-clicking and choose "Increase fee". You can mark a transaction as final when increasing the fee, doing this will make you unable to increase the fee again (after you broadcasted the "final" transaction).
