1) The second transaction doesn't replace the first one since they both are in the pool of unconfirmed transaction. Both are valid until one of them gets confirmed. The reason the higher fee transaction may be confirmed faster than the previous low fee one is that miners are usually incentivized to maximize their profits and strive to include transactions with a higher fee. 

2) The thing is you can't spend part of the UTXO. So if your UTXO contains 3BTC, and you need to buy a cup of coffee worth 1BTC, you end up sending 1BTC to the coffee shop owner and 2BTC back to yourself. That transaction will destroy the old 3 BTC UTXO and create two new ones 1BTC for coffee 2BTC as change. For simplicity, I didn't include transaction fee.

Part of the reason bitcoin is a valuable digital currency is that you can't spend the same UTXOs twice. If there are two conflicting transactions that are trying to spend the same coins, only one of them will be included in a block. The other will get dropped and become invalid. Most likely the second transaction with a higher fee will be included first thereby making the lower fee transaction invalid.

It'll cost you nothing to try and might be the cheapest option.  Your funds aren't at risk.

Once done and it works
Do you control any of the receiving addresses (eg a change address) ? As you could spend the funds sent to that address at a higher rate but if electrum has already forgotten about the transaction it might be harder it set up (unless electrum says "+x btc unconfirmed".

I want to install Bitcoin Core on my computer. Please tell me what I need to know about security, what needs to be done so that no malicious programs spoil my pc and my Bitcoins are not stolen
Thanks in advance!

It's a project I heard the Winklevoss brothers invest in. However, there is a huge difference between the early investors and the current investment figure. I can not believe because of that difference.

It has been a long time since i last ran vmware player (at work, we have power partitions, at home i switched to openVZ for my virtualisation needs a long time ago), but after some quick googling around, you should be able to go to "VM > Settings, click the Options tab, and select Guest Isolation", then disable "drag and drop" and "copy and paste". To disable the network, you should probably go to your network adapters on your local machine and disable the "VMware Virtual Ethernet Adapter". For the local folders: IIRC, the default options would be not to share any local folders, so if you use the default settings the folder sharing should be disabled already.

These are the  things that immediately come to mind... Maybe somebody else will weigh in on this topic and give some more tips and tricks?

Good luck!

In the past, there were vulnerability's in virtualbox that could have been exploited, but the odds of running a virus in a very recent virtualbox vm that's built to exploit any unpatched vulnerability's is very low. You do have to make sure you isolate the VM properly... If your network isn't disabled, a virus could spread over the network, same with shared drives and maybe those drag and drop options...

That being said, malware *could* exhause the host's resources, so it's possible your PC will freeze because of a virus running in a VM container, but this should be harmless...

Running in a VM is better than running in sandboxy afaik... the level of isolation would be a lot better in a virtual environment vs a sandbox on your system.

You can always install vmware player on your local machine, just make sure the network is disabled, nothing is shared, drag and drop is disabled,...

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