i have uploaded my photos in google photos with upload size Original. Now 4.4GB only left out of 15GB. I have deleted photos in my phone after uploading to google photos. Now i changed my google photos settings, i have selected Upload size High Quality. But still it is showing 4.4GB left. I want to keep all my photos in google photos as well as i want to get more free space which is occupied by the photos with Original size.
Go to photos.google.com. Select Options from the top left of this page, then select Settings near the bottom of the Options menu. Change the radio button to High Quality (free unlimited storage). Just under this you will see two options - Buy Storage - Recover Storage. Select Recover Storage and you will be presented with the option to "Compress". Select Compress and it will warn it could take up to an hour to complete. Go ahead and you will have then compressed all your original sized photos to High Quality and recovere the space. If you don't have the full size photo's backed up, be aware this option is not reversible.
You already uploaded them as Original size, so changing to High Quality after the fact it'll still report 4.4 GB free. You'd have to make sure the photos were still on your phone, remove them from Google Photos, then re-upload them with the High Quality setting.
Changing to High Quality after an upload won't affect photos already uploaded in Original quality.