How to Remove the Pixieset Branding "Powered by Pixieset" Message:
To remove the "Powered by Pixieset" message go to Account Settings > Logos & Branding > and locate the "Pixieset Branding" Option, and disable this feature. This will remove the "Powered by Pixieset" message from your Pixieset Homepage, as well as your Collections.
Please note that disabling the Pixieset Branding will not remove the Pixieset Domain from your Collection links.
How to Remove the Pixieset Domain from my Collection Links:
If you're looking to remove the Pixieset Domain (.pixieset.com) from your Collection links, you would want to create a Custom Domain to be used with your Pixieset Account. You can find more information about this here.