If you want higher graphics modes, you need to install Monitors. You drag these from the Storage/Monitors folder into the Devs/Monitors folder. This is in AmigaOS 2.x and higher, so if you're using 1.3, you're SOL.
The Indivision should support most of them, though I've only ever used the NTSC/PAL modes myself. Known to work are SuperPlus (800x600), HD720 (1280x720) and the older HighGFX (1024x768). There's a new HighGFX driver that pushes 1280x1024 (HOW!?!?!) -- no idea if it works or not. These can be downloaded from Aminet.
Out of the box, the Indivision shows the entire Amiga overscan and then some -- you can use up some of it by editing your overscan settings in Preferences. You can also edit the screen mode to have less black around the Amiga screen by using the Indivision ECS tool.
The documentation as well as recent updates are here