How to change the salesperson name from frmSalesPerson

Hi, I gotta change the salesperson name in a customization, there is on web a blog with the next;

Affect the salespersonID of the salesperson which was selected to the retailTransaction and the saleItems of the retailTransaction

But how can I do that?... I've been trying to find the frmSalesPerson in Dialog class but it doesn't exist there.

Thanks!