If you want to remove roles that are allowed to join a giveaway, you can do so via /configure-giveaway update removerole. Simply run the command and select the giveaway and then which role you want to remove from it. Only users that have at least one of the roles designated as required roles for a giveaway will be allowed to participate in it. If no roles are required for a giveaway, it is accessible to everyone.
If the giveaway is holder-based, ownership of the required token at snapshot time is required in addition to having one of the roles.