My landline phone 's ringtone is quite low

Hi, I have a Panasonic landline phone model number KX-TS500MX

and I have problem with ringtone sound, it's low, when someone tries to call me i hear the ringtine but the sound of it is very low, I tried to turn on the ringer swith to the maximum, but the ring is still the same, i tried also to replace the big capacitor which located in its electronic board with new capacitor, but the problem is still accure, can I know how to solve this issue, thanks in advance.