Goto the office and just ask for a Time Off Request form. Fill it out with the day or days you want off and turn it in. If possible make a copy of it and keep for yourself and make sure to give it to the right person. And remind(pester) them several times upto the week that schedule comes out. Don't rely completely on them, CYOA up till the days you want off. If you have any persal hours aquired then you can use them and get paid for it.
If you need personal days off, the reason is personal, you don't have to answer that, like the other guy said fill out the sheet and turn it in, I give mine to the grocery manager, make sure you remind them a few times and even leave a copy on their desk they SHOULDN'T ask you why you want it off, that's why it's called personal, but don't get smart with them, if someone else requests the time off at the same time it comes down to whoever asked first, reasons should not matter.