Our title is spelled the way it appeared on screen, for the first public exhibition, in the native language. If a title was changed for video release, or for release in another country, or for general release after a series of festival screenings, that won't be reflected in the main title -- but the alternate title should appear elsewhere on the page.
Remember that, when you are correcting a title, you are correcting the title across IMDb, not only how it appears on your IMDb page. Therefore, you need to make the correction from the title page. Click on the Edit Page button at the bottom of the title's page, and choose Title Correction from the list. Enter the corrected title on the subsequent page and help is available in this guide.