Ehy guys i'm a noob in this thing.
I have a transaction made from mycelium not confirmed from 2 days now, i'd like to double spend it whit a higher fee to complete the payment, it's easy to do this?
Nope.
You need:
#1 the network to forget about your transaction. If Mycelium is rebroadcasting this means to not use it at all for at least 24 hours. The question came up recently in another thread, but I dont know how Myceliums reacts when a TX does not get confirmed. You should research a definit answer for this to improve your chances of a double spend.
#2 the wallet to forget the TX existed in the first place. I have no clue if thats even possible with Mycelium. If its not possible to modify it with external tools, you have to export the private key into a different wallet. Keep in mind that exporting a private key is always a risk to leak it.
While these two things are difficult, once you managed them you can just create a new TX and set a higher fee.