Here is the link to get the user manual for a Uniden D1760. It will download automatically.
To increase or decrease the ringer volume : when the phone is in standby mode, i.e. not being used, use the up arrow button on the phone to increase the ringer volume and the down arrow button to decrease the ringer volume. Scroll to p.5 in the user manual.
Unfortunately the cordless phone compatibility list from Uniden is not available (file not found message on their website link). You could try contacting Uniden Customer support to verify whether they are compatible or not. Here is their contact details, if you are in the USA of course.
For Product Support on:
Cordless Phones, Bluetooth Products, & Family Radios
1-800-297-1023 Mon-Fri 8:00A.M. to 4:30P.M. C.S.T