If you have uploaded a lot of photos and videos to Google Photos and your storage space is full, then you can free up Google Photos storage usage from Google Drive using computer. Once you signed in to Google Drive account, you will see the storage information in the bottom left corner of the window. You will see the options such as Drive, Gmail and Google Photos and how much space is taken by them. If you want to free up the space, then use the Sort option to see what photos are taking up the most space. Once you sorted them, you can download them to computer and delete those photos.
Here you will see better quality photos have the bigger in size and the high resolution photos in bigger in size compared to the compressed ones. So, when you sort the photos by size, you will see bigger size photos first. It helps you to delete those bigger size photos and free up space on Google Photos.
To do so, sign in to "Google Drive" on the web and click "Sort" icon located at the top right corner. You will see 4 options i.e Name, Last Modified, Last modified by me and Last opened by me. Choose an option and delete the photos to free up space. You can also sort by file owner from the home screen. To do, click "Owned by anyone" and switch to either "Owned by me" or "Not owned by me".