Yes some major changes has been done.. You can always check for new versions in your
wp backend.
Just go to CPAuction --> General Options --> Check for updates.
=== Version 3.1.0 ===
* Added auction purchase by PayPal transaction history.
* Added auction purchase by Bank Transfer transaction history.
* Added auction purchase by Credits transaction history.
* Added credit purchase by PayPal transaction history.
* Added credit purchase by Bank Transfer.
* Added credit purchase by Bank Transfer transaction history.
* Added option to activate/deactivate auctions from transaction history.
* Added option to activate/deactivate and distribute credits from transaction history.
* Added option to enter support license key, with this you will receive automatic upgrades.
* Removed social sharing and category import, these will become paid add-ons.
* Made all payment options available for posting of new auctions and for relisting of auctions.
* We will now start to prepare the plugin for ClassiPress v3.20.
=== Version 3.0.9 ===
* Added use of classipress profile for users.
* Added payment testing using PayPal sandbox.
* Added option for use of credits. Buy credits with PayPal (Bank Transfer will come in version 3.1.0)
* Added setup instructions and help icons in CPAuction General Settings.
* Added Bank Transfer as payment option.
* Users can now relist closed auctions and pay with PayPal, Bank Transfers or credits.
* Post new auctions and pay with PayPal, Bank Transfers or credits.
* PayPal Adaptive payments is disabled due to issue with pay key, i hope to have a fix ready for version 3.1.0.
Yes you should deaktivate and delete old version unless you have paid support license then it will all upgrade automatically.
No data will be lost, only files are deleted so nothing to worry about