I can not go back to original install. Altough I backed-up everything to the other partition and deleted original /.bitcoin folder, everytime I purge bitcoin-qt and re-install it it starts with already made new /.bitcoin folder.
I cleared some space and it's ok if Bitcoin core uses more of it, but I don't know how to continue with synchronozing and not lose payment I got on previous wallet which is backed-up.
On whatever machine you installed Bitcoin core on, go to the data directory (~/.bitcoin) and replace the wallet.dat file in there with your backup wallet.dat file. Then start Bitcoin Core. That is how you import wallets into Bitcoin Core.
Since you are already using Bitcoin Core, I recommend that you continue to use it as switching to another wallet is a hassle.