First up, make a copy (or three) of your wallet.dat. Then you'll need to make a decision regarding your storage options. Can you add a larger drive to your system? If so, then get at least a 500GB, but preferably a 1TB drive and add it to your system.
Afterwards, goto https://bitcoincore.org/ and get the latest version of Bitcoin Core (currently 0.20.1) and install that.
Now, you can read: How to move the Bitcoin Core Data Directory-, so you can move the data directory onto your new, larger, storage drive.
Then simply start Bitcoin Core and let it sync up... it'll eventually finish and you'll have a fully synced node, using your old wallet.dat with the latest version of Bitcoin Core.
If you can't add a new drive to your setup, then your options are:
1. Pruning of Bitcoin Core
or
2. Exporting your private keys from Bitcoin Core and then importing into an SPV wallet like Electrum or Wasabi etc.