How do I request a custody change?

I fucking hate my dad. he's a achoholic who has driven me and my sibling drunk. he's passed out drunk almost every night and I don't want to see him anymore but I'm 13 and don't know how to even request a custody change. I'm 50/50 with my mom and I love spending time at her house. everything is so much easier and better. my mom cooks and my dad gets fast food every night. My mom cleans (I help her ofc) my dad let's the house rot. I can't stand him and I want to have 100% with my mom and I need help knowing how to even go abt that so if you have any advice or know who to talk to I'd really appreciate it. (p.s i have talked to my mom about this but she cant do much because I don't have much proof and of custody laws)