You can delete territories anytime you want in the web application. When you delete territories, the existing records are still assigned to the territory, but new records would not be assigned to it.
To delete a territory from the territory list view,
Go to Admin Settings > Territories.
From the territories list view, click the three dots icon beside the territory you want to delete and click Delete
A confirmation dialog box appears. Click Yes to delete the territory.
To remove the territory from an auto-assignment rule,
Go to Admin Settings > Auto-assignment Rules
Under the Territories section of the rule, click the delete icon to remove the territory.
In the confirmation box that appears, click Yes
Note: If a territory is deleted, users are not removed in the rule. If a territory is removed from the rule, all users are removed.