Hi there and welcome
This is controlled by the Ring Count, it can be 2 to 7 rings.
To change this, pick up the phone and press Menu#211
You can then set the ring count there.
Use the up and down arrows to select then Save to set it.
If you have any problems, or would like any additional information or assistance, please do not hesitate to let me know.
And if you can take a second to rate my service by clicking one of the stars at the top of the screen then submit, that would be greatly appreciated.