Help!

I managed to find some wallet .dat files on my comp that I thought were lost and gone forever! The trouble is I don't know what to do to open them into a wallet. I had been clearing stuff out of my comp years ago and deleted the wallets (I'd bought the coins with my now ex and I was kinda deleting anything to do with him- stupid but true).

I'm guessing to start with I have to download the wallets again, but after that I really don't know. How do I get the wallet to use the old dat file rather than the new one?

I've got a few different coins, so it's gonna take a while to sync everything up.

I have no idea how much I have, could be hardly anything. I'm looking forward to getting into them to have a look.

Thanks for your help