If you have an Android phone, it's easy: just hook up the phone to the computer via USB and transfer files & photos directly.
If you have an iPhone, it's not so easy: you have to transfer the photos to your iCloud account then to your computer; better yet, transfer the photos into your Google Drive then to your computer.
1) To upload the photos from the iPhone to the Google Drive:
* On the computer:
- Log into the Google account
- Verify that the Google Drive is active
* On the iPhone:
- Connect the phone to the power supply (since the process will take some time)
- Connect to a wi-fi source
- Download the "Google Drive" app
- Go into the Google Drive app
- Click on the Menu icon (top left corner)
- Click on the Settings icon (top right corner)
- Click on Backup menu item
- In the "Backup with Google Drive" screen, click on the "Photos & videos" menu item
- Set "Back up to Google Photos" to On
- Go back to the "Backup with Google Drive" screen
- Click on "START BACKUP"
- In the "Backup in Progress" screen, wait for the backup to be done
- When the "Backup complete" screen shows up, click on Done
* Back on the computer:
- Get into the account Google Drive
- Make sure that the "Google Photos" folder is present
- Go into the "Google Photos" folder
- Make sure that all the photos are there
2) To download the photos from the Google Drive to the computer:
* On the computer:
- Log into the Google account
- Go into the "Google Photos" folder
- Select all files in that folder (Ctrl-A)
- Right-click then select Download
- Select the download folder
- Click on the Save button
- After saving is done, can delete the files from the Google Photos folder
* On the iPhone:
- After saving is done, can delete the files from the Camera Roll folder
