Well, as far as i can see you're a Greek, i'm too, but since forum is in English let's first respect the rules.
However about the "conversion" issue, while you have bitcoins you have it on a wallet as you mentioned. So you want just to find out a platform to sell bitcoin or buy bitcoin, that one i am going to give you is using peer to peer connection in order to complete the order.
So there you are, what you need? Simple, you want a skrill or paypal or some platform that you can receive those money on, after you get your money you need to withdraw them into your paypal, skill etc etc account.