How do I access icloud photo gallery to transfer photos?
This is a guess, but if you turn off iCloud back up on the iPhone, you may be able to access them using iTunes from your PC.

To turn off backing up photos to iCloud on an iPhone, go to Settings, then iCloud, then Photos, then turn off iCloud Photo Library. Note: My Photo Stream does not use any of your iCloud storage, so you can leave this on if you want.

Then, go back to Settings, iCloud, then Storage, then Manage Storage, then select your phone. Let it load, then turn off Photo Library under "Next Backup Size".

If you want to delete the photos on iCloud you can do it from Settings in your iPhone. Go into Settings, then iCloud, then Storage, then Manage Storage, then iCloud Photo Library. Use the delete button there.