Adjust Resolution for Raspberry Pi

If you are using Raspberry Pi with the screen, you may encounter incomplete display, with black space around. that would be wrong resolution.
Step 1: Open config.txt
Connect a mouse and a keyboard to your Raspberry Pi. Click open the Terminal, and type in the command to open config.txt

	sudo leafpad /boot/config.txt	

Step 2: Modify the config.txt file
Now the file config.txt is opened.
1)Define a custom CVT mode add the following lines below #hdmi_force_hotplug=1.

       hdmi_cvt=1920 1080 60 3 0 0 0

hdmi_cvt=<width> <height> <framerate> <aspect> <margins> <interlace>

Value	Default	Default
width	(required)	width in pixels
height	(required)	height in pixels
framerate	(required)	framerate in Hz
aspect	3	aspect ratio 1=4:3, 2=14:9, 3=16:9, 4=5:4, 5=16:10, 6=15:9
margins	0	0=margins disabled, 1=margins enabled
interlace	0	0=progressive, 1=interlaced
rb	0	0=normal, 1=reduced blanking

2)Find the following lines (If there is a "#" mark at the beginning of any of the three lines, which means they are comments, delete the mark. The asterisk "*" represents the value.
hdmi_group=*
hdmi_mode=*
hdmi_drive=*
3)Modify the value, like this:
hdmi_group=2
hdmi_mode=87
....
hdmi_drive=2
hdmi_group=2 means DMT (Display Monitor Timings; the standard typically used by monitors)
hdmi_mode=87 indicates the resolution mode we set before.
hdmi_drive=2 selects the Normal HDMI mode.

For more details about configuring config.txt, refer to Raspberry Pi official website: https://www.raspberrypi.org/documentation/configuration/config-txt.md

After the modification is done, save, exit then reboot your Raspberry Pi and enjoy.
http://wiki.sunfounder.cc/images/b/b5/Modify_resolution.pdf