If you are having trouble with Bookshelf on your Android phone or tablet, you may want to remove all of the Bookshelf data from your Mobile device before uninstalling and reinstalling Bookshelf.
Removing Bookshelf's Data Folder
Step 1 - Tap on the Apps Button and tap on Settings
Step 2 - Tap on Storage in the Device Settings
Step 3 - Tap Other in the list, and in the pop-up dialog box, click on Explore
Step 4 - Locate the com.vitalsource.bookshelf folder
Step 5 - Tap and hold on the com.vitalsource.bookshelf folder until it has a checkbox next to it and then tap the trash icon in the top right of the screen.
Step 1 - Tap and hold on the Bookshelf icon until a trash can icon in the top right-hand side of the screen. Drag the app to the trash can to uninstall Bookshelf.
Step 2 - Confirm you wish to uninstall Bookshelf.
Step 3 - Reinstall Bookshelf from the Google Play Store and sign back into Bookshelf