How can I merge Topbar with Header, move "Files" and "Groups" from header to the topbar?

Thanks to Cash and the Elgg team for making great Open Source software ELGG. I would like to merge Topbar with Header, (I do not need two layers)  move "Files" and "Groups" from header to the topbar? 

which file should I modify? should I implement it as a plug-in? Can I remove all of other plug-ins what can improve the code performance?

Many thanks in advance!

Gordon

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Beginning Developers

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