I also wanted to replace the text - "Looking for Something?". If you go into the Language editor of Joomla
Extensions -> Language Manager -> Overrides
Add the variable - COM_EASYDISCUSS_SEARCH_PLACEHOLDER
Place the text that you want instead and save.
Advantage with this approach is that the overrides will continue even after updating EasyDiscuss files.
Note it won't change text size, etc. as above. Just wanted to add here as this thread comes up when doing a google search on how to change it...