Dette nedenstående, er taget fra et Forum, hvor der er folk som har haft samme problem. Jeg har "klippet" dette ud, da mange af de andre svar, nok rammer ved siden af det du søger. men ellers er linket nederst.
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It is possible to make the ribbon smaller (at least it is in Windows 8.1.)
Go to control panel
Click on Display
Underneath "instead of changing the size of everything, click on the item...." click on "menus" in the drop down menu box.
Lower the size from 12 to 8 or 9 or 10 or whatever works with your display.
Restart windows to fully implement display changes - they are not always immediate.
Try this several times and with different items in the drop-down menu. It took me about half an hour and several restarts to get things looking right.
Voila.
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http://answers.microsoft.com/en-us/msoffice/forum/msoffice_excel-mso_windows8/customize-ribbon-size-to-make-it-smaller/58580e49-8104-46e2-a02b-b3ed47319409?auth=1