download a file manager app with root permision( recomended root explorer)
in then root tap,go to system an hold the build.prop file and chose open with text editor
then find "ro.sf.lcd_density=xxx(value)" and change it
after that,save it and delete build.bak or build.prop.bak( for root explorer ) and reboot
I recomended just to change the values higher/lower the original for about 30dpi so you won't face bugs
