Default View Change
The affiliate panel menu and menu contents can be managed in the merchant panel from Configuration > Affiliate panel in Menu & screens tab.
On the right side you can see menu items which can be used in the affiliate panel.
Each screen which contains a grid (Subaffiliates sales, Top referrer URL, Channel stats report, Subaffiliate Sale Stats, Commissions, Raw Clicks, Payouts to me) has its own view (number of columns shown, type etc...) and you can edit it (Edit button) in the tab for editing the default view.
Here you can define the default view for affiliate screens:
If you do not want to allow affiliates to change the default views in their grids, read this
Remove Columns from Grid View
If you would like to remove some columns from the grid view, then you can do this in the 'Transaction List Allow View' tab. For example, you don't want your affiliates to know the total cost of the commission, then you can remove the Total Cost column:
Don't forget to click 'Save'
at the bottom.