One way you can get free wallpapers on Macs is by downloading an app called Free Wallpapers Lite and downloading some off of there. You could also try to find another app offering free wallpapers as well.
You have to do it on a computer. I don't think you can delete it directly from the Nook.
you cant it never comes off
1. Put finger on the app you want to delete 2. Hold finger there until the app starts vibrating 3. Press the "x" that appears on the top left side of the app 
To delete a mixtape from the My Mixtapez app, open the app and navigate to your profile or mixtape library. Find the mixtape you want to delete, tap on it to access the details, and look for an option to delete or remove it. Confirm the deletion when prompted. If you encounter any difficulties, consult the app's help section for specific guidance.
Try to delete the App
Complete the download and then delete it from your home screen
go to the contacts app click the contact that u want to delete press edit then at the very bottom press delete contact
Turn it off or delete it
hold an app and the apps will start to jiggle with an "x" above, click the x and the app will be deleted.
Settings > General > Restrictions > Type in the code you want to use > Deleting apps > Off
Are you on restrictions? Go to settings, general, then turn off your restrictions.