Create testing plan (how to ensure that the new upgrade works without affecting current system and no data lost.)

You are a software developer for a Retail Point of Sale System Company. A client has made a request to upgrade the current system from command line interface to a graphic user interface. The client concerns on an effect to the current system with the change. The client does not want to lose any current data on the system. Provide recommendations and the change plan including the below requirements to the customer.

Requirements:

Create a requirement plan (what need to be done to support this upgrade)
Create a development plan (how to implement this upgrade with programming details explanation including technical details on this document)
Create testing plan (how to ensure that the new upgrade works without affecting current system and no data lost.)
Posting your recommendations and the change plan
Once you have completed your recommendations and plan. Create a new thread with your plan title and name in the subject line. Your posting must include recommendations, a requirement plan, a development plan, and a testing plan.