You can format an Eye-Fi card like any other memory card. Formatting will not delete any wireless network settings, but it will delete the Eye-Fi Center Software installer as well as any images on the card. If necessary, you can download the installer application here. We recommend formatting your Eye-Fi card in an Eye-Fi Compatible camera if possible.
If you format your Eye-Fi card in a computer, please use the Eye-Fi USB card reader. We do not recommended using 3rd party card readers that have slots for multiple types of memory cards (such as SD and CompactFlash in one reader). These card readers can cause issues similar to using Eye-Fi cards in CF adapters.
The SD Association has free software to format SD cards in computers, which we recommend using to format cards in a computer.