Change google photos picture quality?

I made a new gmail a few months ago and set it up as the one to back up my pictures and videos. Instead of selecting the data saver option I kept it as original quality and now my storage is full. Is there a way to convert these into the lower quality version? Or do I have to delete it all then back them up at the lower quality? Sorry if this is the wrong sub for this, but I do have an up to date S20. Thanks.