Multi-unit pottery kiln - how hot can it go?
If the kiln is rated for 1950 degrees Fahrenheit, then that's about the highest you should fire it to.  The number of rings you use isn't a function of how hot it gets but more a function of how much space the inside of the kiln will have.

To test the kiln, you can just plug it in and turn it on, if it heats up, it works.  As BrownRedHawk stated, you should place some cones in the kiln when it fires to see how hot it gets.  Sounds like your kiln will probably easily fire to cone 06 to 04.