Thanks @odolvlobo
I did step 1-3, but unfortunately I am struggeling at step 3. (https://bitcointalk.org/index.php?topic=2059111.0)

I am following this guide in order to find my private key:

1.Launch your bitcoin client
2.Click on 'help' in the menu bar (top right)
3.Click on 'debug window'
4.Select the 'console' tab
5.If your wallet is protected by a passphrase (i.e you have to enter a passphrase before you can send) unlock it by typing
walletpassphrase "your walletpassphrase here" 600
dumpprivkey [your Bitcoin address here]
This will return the private key which will start with the number 5

The problem is, how can I find my Bitcoin address for step 5 "dumpprivkey [your Bitcoin address here]", I used so many different addresses for receiving and sending. I really would apprecciate any help.
Thanks.