Estimate, Invoice, Bills, Purchase order, Sales Order, Delivery have the Salesperson option. You can set a salesperson based on your business and branches, as default under the settings option, instead of selecting the salespeople all the time while creating those transactions.
Goto Settings > Business settings > Preferences > Sales Persons
Click on salespersons,
Sales persons dialog box opens, then click on Add Sales Person
Enter the sales person name and click on Save to save the sales person.
To edit the salesperson, click on the edit button, a dialog box opens. There you can update the salesperson and click on save to save the changes.