Car Sales MSM in Visual Studio

Everything work except 'Update' code and i can't fix, i give upI mean to finish all the system

They are Customer, Maintenance and Sales form. Connect all with database and count the profit.

Basically the system must allow the user to add, delete, insert and search car or customer. Also to allow to add which salesmen sale which car. And last to count the profit for one month and one year.

Also Update the car details or customer details