I assume you mean the header when reading kepubs. If so, you can enable full screen reading. In the "Kobo eReader.conf" file, add:
Code:
[FeatureSettings]
FullScreenReading=true
This will add an option in the Reading settings to hide the header and footer. Selecting the option will do what the option says. This is an incomplete and unsupported feature. There are some problems with it that can be solved with some patches.