Hi Dannydude_97 - your new plan is already in affect. So on your next bill you will see proration from the day that you switched until the end of your billing cycle + one month in advanced. Also remember that airtime & fixed data amounts are prorated as well.
Your new plan starts Immediately but the amount of data and minutes will be prorated for the next 4 days. So you'll take the amount of data & minutes and divide them by 30 days & times that by 4 to find out how much of each your allowed for the next 4 days. If that's confusing just start using data in 4 days lol