Change or add organisation Logo at Top Left of Agent Browser UI

Summary

One of the businesses using an interface has changed logo and i need to update the current logo at top left.

Content

I have used the instructions seen in the link below however i am unsure of step 5 or 6 b. 

How and where do i store the photo to get the necessary URL into the default box?

https://documentation.custhelp.com/euf/assets/devdocs/buiadmin/topicrefs/t_bui_Change_the_brand_logo_on_the_Agent_Browser_UI.html

Version

20B