How do I resign from my casual position?

I have been working at a franchise fast food store for a little over 3 months now as a casual. I do not enjoy the job, I am not being given fair shifts, I have been wrongly accused of often being late, the uniform I have been provided with is worn and ratty-looking and I do not receive regular payslips. As the owner refuses to hire more staff, even though we are understaffed, I have missed out on a different job opportunity (even though I was assured that allowances would be made before I took the position) because there was no-one to cover my shift. For me, this is the final straw. Everyone I know is telling me to just walk out, but even though I was not treated well, it was my first job and I don't want to be unprofessional. How do I go about resigning in a professional way?