Can I change my no contest plea to a plea of not guilty?

Dallas TX. I'm on a crowded and narrow street when a officer yells at me to "Get out of my ***** way". I tell the office not to swear and he detains me. The officer verbally and physically abuses me (Yes. I have filed a complaint with Internal Affairs and it is being investigated). After questioning he releases me. I demand his name and number to file a complaint but he arrests me & ignores my request. I'm never read my rights or explained my charges. I can't contact my family because there are no long distance calls allowed and no collect calls allowed to cell phones but my family has both. I spend 16 hours in jail before hearing my charges 1) public intox 2) pedestrian in HWY 3) fail to id. All are 100% not true! I'm handed a paper to sign guilty, no contest, or not guilty. I'm so distressed. I've been unlawfully detained, I have no legal aid, I have not contacted any of my family, and I haven't slept or ate. I sign no contest only to get out of jail. Can I change my no contest plea?