A little more info here? What are you looking to upgrade? OS, apps? If it is the OS see the following: BlackBerryOS 4.x Download FAQ - UPGRADE DOWNLOADS and kindly search next time. You can use the OS upgrade from another carrier that offers/offered your model eg. T-Mobile. Note you can probably load 4.0.x.x on you 7230 there's not enough memory to run anything else.
As noted if you take the time/effort to search there is a host of info to help.
1. Disconnect your BlackBerry and close the desktop manager
2. Install the 4.0 .exe file
3. Search your computer for the Vendor.xml file
4. Delete the Vendor.xml file
5. Launch the desktop manager
6. Connect your BlackBerry, you should Be prompted to upgrade.