If original DVD, you can easy rip it and get movie without any titles. Later use some DVD authoring SW to add new subtitle. If subtitles already "engraved" in the picture, you will have to cut the picture to get rid of old subtitles or past new subtitles which have black bacground.
I don't know how to inster screenshots, so here are links to see pictures I WANT TO THIS... http://my.afterdawn.com/lazar95/show_image.cfm/14579/slovenski.jpg ...CHANGE TO THIS... http://my.afterdawn.com/lazar95/show_image.cfm/14580/srpskiprekriveno.jpg ...OR THIS! http://my.afterdawn.com/lazar95/show_image.cfm/14581/srpskinovo HOW TO INSERT PICTURES? PLEASE NOTE that subtitles engraved movie.