Was trying to update my bitcoin wallet after many months (24 months) although the PC has now run out of Hard drive space, and the BTC software seems outdated, what is the best way to get the wallet up to date. (i have located the wallet.dat file on the pc)
Considering you're talking about wallet.dat, then I'll assume you're running Bitcoin Core.
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.