If you wanted to do this with one of your own maps, then you would follow this guide. However, if you're talking about a previously-ranked map, then nothing can be done (yet). Broken or otherwise incorrect artists/titles will be fixed in the near future!
As I mentioned already, I've finally uploaded the map http://osu.ppy.sh/s/35525 In both title and source was a "é", I changed it to "e", now everything is alright