Problem changing Gridmarket Header logo for multisites.

Hi, I have a problem changing the default header logo on my website. I was able to easily upload and change it on my site http://www.cornertheegyptianmarket.com, but I want the same logo to appear on the multi-sites as a default. For example, on http://www.jafar.cornertheegyptianmarket.com the “Gridmarket” text is still showing. Where in the coding would I have to go to change this so when a user signs up and gets their own sub-domain to the site my custom header automatically shows up and not the “Gridmarket” text?? PLEASE HELP!!

Thanks,

Jafar

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