Ozij gave you good instructions.......but, I have a small difference of opinion.
Rather than set the machine "wide open"....from 4 cm to 20 cm.......I suggest that you might feel better with the lower end set on at least 6 cm.
My reasoning is that 4 cm might make you feel that you aren't getting enough air.
I started out with my machine set as Ozij suggested.....and I quickly found that I couldn't handle 4 cm. I later read that 9 cm seems to be the most common setting for most people who need CPAP therapy.
As a side note, I helped my honey self-titrate......and we started at 8 cm on the low end......with the high end set on about 16 cm. After about a month of experimentation, she found that she needed settings of 11 - 14 cm for her therapy to work well.
Also, you need to know that the M-Series Auto with AFLEX has a "Ramp" feature. You can set the machine to "ramp up" to your lower setting....starting, for example, at 4 cm....and moving up in pressure to a higher pressure over a period of 10-minutes......15-minutes.....or whatever time span you're comfortable with.
Finally, I urge you to purchase the "Viewer" software with Card Reader. Without software to give you a recorded chart of how your pressures changed during the night....and some indication of "why" they changed, it's tough to self-titrate. This is not money wasted......because your mother will also find it very useful.