Hi Agnes, yes, you can delete Semester 1 first before you download Semester 2 on your iPad.
Just follow these steps:
1. Open Little Reader Touch and go to [DOWNLOAD LESSONS]
2. Tap "Downloads" from the black menu bar at the bottom of the screen
3. Find English Semester 1 and tap the [REMOVE] button for that lesson
4. When the button changes to say [SURE?] tap it again to confirm
5. Little Reader Touch will delete Semester 1 within a few seconds
As soon as the delete process is done, you may proceed with downloading Semester 2.