ScreenSize Mod 1.7.10 is a great utility mod that will help you change your resolution both in fullscreen and windowed!
The default key to access the gui is the + on the number pad; this is a configurable key.
Press it and you are greeted with this gui:
The errors are actually helpful:
ScreenSize Mod Installation
- First you need download and install Minecraft Forge.
- Then download this Minecraft mod file at link below.
- Go to %appdata%. It can also be found by searching for “%appdata%” in your start menu.
- Go to .minecraft/mods folder.
- If the “mods” folder does’nt exist in your PC, you’ll need create one.
- Then drag and drop the downloaded .jar (or .zip) file into mods folder.