Just download a file Explorer that supports root functions, like En file Explorer. Go to /system/build.prop, open it, search for ro.sf.lcd_density which should be set to 320. Change it to a lower value to have more space, or to a higher value to make everything bigger.
Alternatively if you want to change the density just for a few apps, install xposed installer and xposed app settings. App settings will allow you to change the dpi for each app separately.
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