You can edit an existing Field at any time. The changes will be applied to all new and existing Cards that contain that Field.
Edit a Field:
1. Click your avatar on the bottom-left to open the User menu.
2. Select "Project Settings".
3. Click on the "Fields" tab. All the Fields for your Project will be listed.
4. Next to the Field you want to edit, click the three dots and select "Edit". The "Edit Field" dialog will open.
5. Make your desired changes.
The editing options will depend on the Field Type. The example below is a Single Choice Field. I can change the Field name, I can add or remove values, I can change the value names, colours and order. I can also convert it into a Multiple Choice Field.
6. Click "Confirm" to save changes.
For more help on fields see the Fields Help Guide.