Now open Google Photos app.
Tap the three dashes in the upper left corner. Select settings.
Look for Google Drive and make sure the slide switch is on. Next tap Back up & sync. Make sure the slide switch is on there as well. If you have added camera apps you made have additional folders that contain images. if so tap on Back up device folders and activate the slide switch.
Now give it a day or so to back up your pictures.
If all this was already set you can go back into settings. Your ready to free up space.
So here is the part that will free up storage space on your phone.
Go back into settings and tap Free up device storage. Or on the previous menu Free up space. A pop-up window will tell you how many files photos and videos will be deleted. It will also tell you that the pictures have been safely backed up to your Google drive.
So you can easily free up hundreds of megabytes of space on your phone or tablet with this feature. I hope you found this helpful.