In Shelxpro, use option [M] and follow the instructions:
For a 2Fo-Fc map, it is actually better to make
a Sigma-A type map. For this, you will be asked to supply the reference/working
set Sigma-A ratio which appears at the end of the .out file.
I've had difficulty generating maps on the Alphas and having O read
them, so you are advised to run Shelxpro on an SGI when making map files.