There are several theories and models related to business process improvement that you should study for the Management optional subject. These theories and models provide frameworks and guidelines for identifying, analyzing, and improving business processes. Here are some of the key theories and models:

1. Total Quality Management (TQM)
TQM is a management philosophy that focuses on continually improving the quality of products and processes. It emphasizes customer satisfaction, employee involvement, and continuous improvement. Key concepts in TQM include quality control, quality assurance, and quality improvement.

2. Lean Management
Lean management is a systematic approach to identifying and eliminating waste in business processes. It aims to create value for customers by reducing non-value-added activities. Lean management principles include identifying value, mapping the value stream, creating flow, establishing pull, and striving for perfection.

3. Six Sigma
Six Sigma is a data-driven methodology for improving business processes and reducing defects. It aims to achieve near-perfect quality by minimizing process variation. The Six Sigma approach involves defining, measuring, analyzing, improving, and controlling processes (DMAIC).

4. Business Process Reengineering (BPR)
BPR is a radical approach to process improvement that involves rethinking and redesigning business processes from scratch. It focuses on fundamental changes rather than incremental improvements. BPR often involves the use of technology to automate and streamline processes.

5. Kaizen
Kaizen is a Japanese term that means "continuous improvement." It is a philosophy and a set of practices that encourage small, incremental changes in business processes. Kaizen emphasizes employee involvement and the use of data to drive improvements.

6. Theory of Constraints (TOC)
TOC is a management philosophy that focuses on identifying and managing the constraints or bottlenecks in business processes. It aims to optimize the flow of materials and information through the system by identifying and addressing the most significant constraints.

7. Agile Methodology
Agile methodology is an iterative and incremental approach to project management and process improvement. It emphasizes flexibility, collaboration, and customer feedback. Agile methods, such as Scrum and Kanban, are widely used in software development but can also be applied to other business processes.

8. ISO 9001
ISO 9001 is an international standard for quality management systems. It provides a framework for organizations to establish, implement, maintain, and continually improve their processes. ISO 9001 certification is often sought by organizations as a demonstration of their commitment to quality.

By studying these theories and models, you will gain a comprehensive understanding of different approaches to business process improvement. Each theory or model offers a unique perspective and set of tools that can be applied in different business contexts. Understanding these theories and models will enable you to analyze and improve business processes effectively.