해상도를 높이다 (Note: "해상도를 향상시키다" is also a correct and slightly more formal alternative, but "높이다" is more commonly used in everyday contexts when referring to increasing resolution of displays, images, etc.)

이 이미지를 4K 해상도로 업그레이드해주세요. (Explanation: This is a natural, polite translation of the original request. "이 이미지" means "this image", "4K 해상도로" means "to 4K resolution", and "업그레이드해주세요" is a polite way to ask someone to upgrade something for you.) If a more formal tone is needed (e.g., in an official instruction), it can be: 이 이미지를 4K 해상도로 업그레이드하십시오. But the first option is more commonly used in everyday requests.