How to make a bachelor thesis out of optimizing /updating an application? I work for a company and want to write my bachelor thesis there. This company has a Quality Assurance Application written in Python, that is very unstructured and follows no design pattern.
My job would be to restructure the Application into a layered architecture, and possibly get rid of the GUI and completely automate it.
My question now is how do I make a bachelor thesis out of this?

Write about software design/architecture and use this as proof of concept?
Write about improved speed and improved future maintenance (kind of hard to measure)?
The usual, and normally a good, way is to get an advisor at the university if you don't already have one and discuss this with them. It could save you a lot of grief later and their advice would be more valid in your circumstances than mine.
You may also need to discuss this with the company in case any trade secrets are involved in the application.
But, in general, reimplementing a legacy application using modern design patterns and/or improving performance and/or providing better UI is not a bad idea.