Can I adjust my photo so I can enlarge it with it being grainy?

There is only so much detail in any given photo. if you enlarge it past a certain point, you will start seeing artifacts ("grain").

There are programs that can use artificial intelligence techniques to suppress that effect by approximating a smooth picture. That's not a feature of the Photos application, though.

It really depends on the details, the more pixels you start with, the better the results. You can't do much with a typical avatar image!

Full blown graphic programs often have several enlarging algorithms that have varying degrees of success. Sometimes it helps to enlarge in steps.

Do not expect Blade Runner or NCIS levels of sharpness when enlarging.

When I want to enlarge a photo, without it becoming blurry, I am using the free online image enlarger. It is offering ten different algorithms to enlarge an image without losing the sharpness. You can compare the results for the different methods and download the most pleasing result. Online Image Enlarger

What is happening that you see it grainy?

Keith and markwmsn are answering if you are meaning you want to make a 16x20 inch print from a fuzzy image off a web page. Is that what you need, or are you concerned that a recent iPhone image looks grainy?

How important is this to you? What's your budget for the job?

https://www.topazlabs.com/gigapixel-ai