I have a number of C files with tab indentations that I would like to convert to 4 spaces/tab. But, I cannot figure out how to do this.

If I go to Document -> Indent Type = Spaces and Document -> Indent Width = 4, any NEW tabs are space filled. But, the old tabs are NOT. So, if the document is viewed in ant other text viewer with tabs set to the default 8 spaces, the program alignment and indentation goes out of whack.

What am I missing?