Login via ssh:
ssh -2 user@domain.tld
sudo -i
Copy Your logo white template:
cp /yourlogo.png /var/packages/PhotoStation/target/photo/photo_new/images/White/logo_ps6.png
Copy Your logo dark template:
cp /yourlogo.png /var/packages/PhotoStation/target/photo/photo_new/images/Black/logo_ps6.png