How do I level charisma?
I know speech is by talking, but while I have 15 charisma or so I still can’t figure out what I actually did to level it up.
Your attire, dirt system(You need to bath yourself and wash clothes and etc.) also sleep and other stuff. Some perks do affect this param. like Shining knight (+3 for charisma at day time, if you’re wearing plate armour). 
There’s no leveling for charisma. Its just hard on your outer appearance
But I didn’t start with 15, and now even when I take off all my clothes it’s just that. My armour and such makes it go up to 20.
Speech skill increases base charisma. Various perks and buffs do too.