You can control your coins in Bitcoin core without needing to wait for the sync. It is not easy and you should test it (testnet or another wallet with small amounts) until you know what you are doing.
I can't give you a complete tutorial, but try searching by keywords. For more security you can use a Linux LiveCD btw.
(No need for an internet connection)
1. Encrypt and backup your wallet.dat (multiple backups is better and NEVER EVER FORGET YOUR ENCRYPTION PASSWORD)
2. Open Bitcoin Core Console (no need to be syncing. )
3. Export private keys (This is pretty complicated for beginners, but done in a few seconds by someone that is experienced. You will need help here or test it until you are safe)
4. Install Electrum wallet (
https://electrum.org/#download )
5. Import Private Keys from your Bitcoin Core wallet
6. Now you need to be online to let Electrum sync, which needs a minute or so.
7. Spend your Bitcoins.
Good luck
edit: To understand the main concept of Bitcoin I would recommend this one for beginners:
Bitcoin 101 - Quindecillions & The Amazing Math Of Bitcoin's Private Keys
https://www.youtube.com/watch?v=ZloHVKk7DHk