From the Quote Summary page, click the $ Adjust button.
Here you can adjust the total amount payable for all items within the quote by increasing or reducing your commission.
From the three fields available you can apply a discount by a:
Dollar amount
Percentage amount
Or, set total customer amount payable
Note, you can use these fields to add fees too, so be careful to include a 'minus -' if wishing to discount, i.e:
Add a minus amount for discount, i.e -$50
Add a positive value to add a fee, i.e $50
Once applied, adjustments will be applied pro-rata to all products within the Quote. View adjustments from the Products tab within your Quote Summary.