You're not going to like this much. This model only has 2 rings, 4 rings and TOLL SAVER which answers on the 2nd ring if you have messages and the 4th ring if you don't.
A lot of the Vtech models adjust from 2-7.
Here's the manual, check out page 28 (32 pdf). http://www.uniden.com/pdf/EXAI918om.pdf