I have severe sleep apnea and have a cpap machine.it used to work great buy now if i start it i feel like i'm suffocating.can i change settings legall?

Definitely: You can definitely try to adjust settings. Let the company know as well as your physician. Another possibility may be that the mask does not fit anymore and that' s why you cannot tolerate it. The answer will be provided by a titration sleep study.

Sleep apnea: No you should not change the settings but you must see the doctor who set the initial instrument.

May need titration: Call the company supplying the CPAP and they can do a titration to get the optimal setting.