There are a couple of ways you can do this. This is how I'd do it in Electrum:
1) Replace by fee - In electrum there's the ability to go to "If fee is too low" or "Always" from Fee preferences in Tools. This would've then let you select 'Replacable' to allowed you to later on replace the fee of your existing transaction. Could you check if Mycelium allows this feature? I'm not sure since I haven't used that wallet. I believe I was able to do this in electrum by right clicking on the unconfirmed transaction -> selecting increase fee --> then setting a higher fee or using electrum's dynamic fee that was already set.
2) This is possible now if you're receiving the funds - Child-pays-for-parent - In the 'History' section right click on the transaction that is unconfirmed and then selected Child pays for parent -> increase the fee this time to a suitable fee (calculate it from here:
https://bitcoinfees.earn.com/) -> Sign and broadcast the transaction.
3) By using a transaction accelerator like confirmtx, viabtc's tx accelerator or antpools tx accelerator. I've accelerated your transaction on confirmtx and antpool's accelerator. It might get confirmed in upcoming blocks when they include your tx in their block that is mined. If you can't wait for this option to have your tx confirmed, follow option 2 if you're receiving the funds.
Edit: Updated post after confirmation.
Hello xdrpx and thanks for your reply!
1) If I read correctly, RBF is an option I can activate for future transactions? I will definitely look into this and making sure I have a high enough fee for any of my future transactions. I work with Electrum, not with Mycelium. When I right-click on the unconfirmed transaction, I don't see the 'selecting increase fee' option.
2) I am the receiver of the funds, but on the Kraken account. When I right click on the unconfirmed transaction in Electrum, I do see the 'Child Pays For Parent' option, though. Should I try this out?
3) Thank you for accelerating my transaction. I have tried so myself through ViaBTC, but could never get through. I did read somewhere that this form of 'bumping' is overcrowded a lot these days. I could wait a bit to see if this works for me, though.
Thanks again for helping me here!