The best way to do it before/while filing I-485. Just put the name you want on the application and list all other names in “names used” field.
Also – provide all necessary evidence of name change for whatever reasons you do it.
You’ll get your receipt and then GC with a correct name – the one you want.
If you wait till you get your GC to do it – it might cost you more money and cause extra troubles.
When I filed for GC I didn’t change my last name to my husband’s, I just added it up… later I changed my mind and got my last name changed on every document (SS, bank accounts), except DL. When I finally got my GC I went to DMV office to change my DL and I wanted to change my last name to my husband’s there as well, but they wouldn’t do it – they said they will print it exactly like the INS did. And they did and now I am stuck with double last name until naturalization (I don’t want to file I-90, I can wait, not a big deal it’s just annoying at times).