Install/upgrade the B2latex plugin from the Main Rodin site using the software updates menu in Rodin.
After installation, you will see an L button on the menu bar in the Event-B perspective. Select the Machine or Context you want to translate to Latex and then press the L button. A latex source file will be generated in a folder named Latex in your Event-B project directory. bsymb.sty is required to process the latex. Run latex on the source files using your own latex installation.
The file b2latex.sty in the generated Latex directory can be modified to change the style of the documentation.