On the charging screen, touch Set Charge Limit, then slide the limit along the battery graphic to anywhere you want, typically 60-90% or 100% for max charge. Now the charging will stop at that charge level in your battery.
Changing the amps on the charge screen will change the rate at which the battery will charge. If you're at the max amps for your car and it shows that it will take 4 hours to charge, then lowering the amps to half the max amps will increase the charge time to about 8 hours.