You can actually follow the guide link from Charles-Tim, but I don’t think that actually removes the unconfirmed transaction because as you know an unconfirmed transaction cannot be removed, what is basically done is you’re double spending same transaction and since the new one would have a much higher transaction fee it gets confirmed first and then invalidate the first one. Even if you delete the local transaction and didn’t broadcast a new one it will still be there and could get confirmed later if the mempool congestion reduces before it is totally dropped from all nodes
What I noticed is that if the coin is dropped due to mempool congestion making the purging to be greater than the fee rate used, or the transaction is getting longer than 14 days that most nodes would have dropped it, some nodes can still have it because nodes can change the default settings. That was why I am not surprised when a transaction I made dropped from mempool of a node but I was still able to accelerate it using ViaBTC free accelerator.
But if you replace the fee using opt-in RBF, the transaction will drop from mempool of other nodes.
For full RBF, I am not certain about it and you may be right. But I am not sure.
It used to have an option for RBF in the preference section but it seems now it's not there. I guess RBF is now a default setting for Electrum.
You are referring to opt-in RBF. But this is about Full RBF. Electrum remove the option and make all transactions to be flagged as opt-in RBF since version 4.4 or so which was some months ago in last year. So all transactions made on Electrum now all support opt-in RBF.
