To do the thing you're asking for in this thread, select the entire map, press CTRL-M. Then click the "scale" option and type what you want to scale the map by in each direction. This will probably take quite a while to compute.
To do the thing you should do instead, remake the map's brushwork where you think it is too large. This will take more time, but will obviously give better results since it'll be tailor-made rather than scaled overall.