Custom fields are only available to customers on the Enterprise tier.
1. To delete a Custom Field navigate to Settings - Data Dictionary and hover over the table related to the field you wish to delete. In this particular example, we will delete a custom field related to the Asset record, so we will select 'tblAsset'.
2. Hover over the field you wish to delete and select the trash that will appear to the left as shown below.
3. Confirm to delete the Custom Field.