Saved views in the sidebar are kept as long as they are useful. You can rename them when their purpose changes, update their filters if the criteria evolve, or delete them when you no longer use them.
Rename a view
Hover over the view in the sidebar.
Click the three dots (…) that appear to the right of the name.
Select "Edit name", write the new name, and confirm.
The same menu also has "Edit icon", to change the view's icon.
Edit the filters of a view
When the criteria of a view change (for example, you want to review the last month instead of this week), update the filters instead of creating a new view:
Open the view from the sidebar.
Adjust the filters in the bar.
Click "Update view". The previous filters are replaced by the new ones.
Delete a view
Hover over the view in the sidebar.
Click the three dots (…).
Select "Delete view" and confirm.
Deleting a view only removes the sidebar shortcut. The conversations that appeared in that view are not deleted or modified.