Update table via customisation

I would like to update GLJrnDtl table. The field I want to update is CheckBox01. I want to do this from some of UDxx form. I know that I need to call an update method. But Update method doesn't have an argument to pass and I don't know from where it takes the data that will be updated. Do I need to create a DataView and update will be updataing data from DataView? If so then the correct way to update data will be as following:
Create a DataView
Get rows from DB
Put choosen row to DataView
Change required field in DataView
Call Update method

Maybe someone have an example how to maku such update?.
Any help welcome.