Select a field from the list to open the field card. Pull it up, and you'll see the 'Edit or delete field' button at the bottom. Tap it to see the 'Delete from this season' option. All done!

In the 'Fields' tab, select one or more fields from the list and click 'Delete'.

Or, click 'Delete field' from the field card in the top right menu.

Or, go to the 'Edit field' tab of the menu and select 'Remove field from ...'.