Which ROM are you currently using? There isn't much difference between these firmware customizations anyway, especially not between the generic (unbranded) ones. However, if you really want to change to a different customization, there are two possibilities:And Where Can I get it?
1) Download an FTF of the customization you want (if available) and flash it with Flashtool.
2) Root your tablet temporary (without unlocking the bootloader) and follow this guide to change your customization number. After that, you can update or restore with Sony PC Companion to download and/or flash the new customization. After flashing, the root will be removed again.