Dangze,
I'm not sure if you're still looking for this information, but he might have done it this way (requires root):
http://www.androidauthority.com/nexu...let-ui-100888/
UPDATE: Just confirmed this works. Here are the steps.
1. Root the Arc.
2. Open /system/build.prop in some rootable text editor.
3. Change the ro.sf.lcd_density to 170.
4. Reboot, and enjoy.
The only downside is that the icons and text are slightly smaller, but now we have LOTS more space on the screen!
You can easily see that if you revert to the stock 213 for density.