Search module - chose category via checkbox

In OS search module I would like to change how the category is chosen. I would prefer check-boxes or the same as it is on the search menu page. Where you can chose the categories of interest. Where and how can I change this?
Thanks

Is there a solution to this? How can this be done?

Hi Davor,
Currently, we are very busy to solve the problem after my site (joomdonation.com) was hacked on 27th Nov. I don't have time to implement this feature. But i promise in the future, when i have time, i will implement it.
Thanks
Dam