How to change settings
To Adjust Google Photos Backup settings:
Look for the Google Photos Backup icon in the system tray on the bottom right:
It may be hidden, if so click on the up-arrow to the left of the system tray to show the hidden icons
Click on the icon and select "Settings..."
Make sure it is signed in to your Google account associated with Picasa
Make sure the folders you want to backup are listed and selected, or unselect all of them if you don't wish to use Google Photos Backup at the moment.
Make sure you have not selected to upload from Cameras and memory cards unless you really want that.
Under "Photo size" choose either of two photo size options:
High Quality - Free unlimited storage up to 16 MP, larger sizes resampled. Great visual quality at reduced file size.
Original - Full resolution that counts against the quota of your Google storage space, so you may need to buy additional storage.
You can also choose to back upload RAW and PNG files
To pause the backup if the program is slowing your computer too much: Click the Google Photos Backup icon then click "Pause backup"