Just to be safe, we recommend saving a backup of your vocabulary to Dropbox, Google Drive, or your computer first. You can find step-by-step instructions in the Protect, Recover, and Share Vocabulary support section.
Once you have saved a backup, make sure your device’s iOS is fully updated. For instructions, see http://support.apple.com/en-us/HT204204
Then, you can update Proloquo2Go manually by following these instructions from Apple: https://support.apple.com/en-us/HT202180
You can find more information in the section Protect, recover, and share vocabulary.