if you owe money for a leased vehicle, if they find anything wrong, can l make payments on wht l owe or do l have to pay upfront? l know l went over the miles, so l know l will have to pay for that

They will want the money upfront. If you owe a lot you may be able to get a loan so that you can make monthly payments. Or you have the option of buying the car.

You can finance those ''charges'' by rolling them into the next vehicle, or u can pay them up front before u move on to the next car. You can avoid making those charges by buying the car at lease-end as well. The other option is to trade-in ur car, but u will be responsible for the negative equity, which can be rolled into a new car payment or u can pay it off upfront.
l normally recommend paying off any fees/charges u owe upfront. It gets expensive to roll in negative equity into a new car.