Q: Manage my photo library

Hello Koch,

It sounds like your iPad is running out of storage and you want to free space on it.  Note the act of backing something up doesn't delete the originals from the device being backed up.

To see if you can free up other data See how much storage you've used on your iPhone, iPad, and iPod touch - Apple Support

Note it links to the article Delete music, movies, podcasts, and other content from your iPhone, iPad, iPod touch - Apple Support

To delete a photo from your camera roll…

• Delete a photo. Select a thumbnail, then tap .

That is from Manage photos - iPad User Guide

Of course you should also backup your important photos to your computer as well.

How to back up your devices using iCloud or iTunes - Apple Support

Take care