Which of the following is used to improve security and overall functionality without losing critical application data?

Patching is the process of applying updates to software to fix bugs, improve performance, and address security vulnerabilities. This directly improves security and functionality without deleting or altering critical application data, as the intent is to enhance the existing system. Reformatting involves erasing all data and reinstalling the operating system, which would result in data loss. Decommissioning removes a system from service, not improving its functionality. Encryption protects data confidentiality but doesn't inherently improve functionality or fix vulnerabilities; it's a security control for data at rest or in transit.