Not everyone is eligible to file Form I-485, Application to Register Permanent Residence or Adjust Status, to adjust status and receive a green card.
The main requirement is that an applicant must be physically present in the USA after being lawfully admitted or paroled into the USA. The other eligibility requirements for adjustment of status vary depending on your immigrant category. These immigration categories include: family relationship; employment; student; K-1 visa holder; refugee; asylee; Cuban national; Panama Canal Zone employee, and physician; Polish or Hungarian parolee; certain US armed forces members.
Applicants living outside the United States are not eligible to file Form I-485. They can adjust status to a lawful permanent resident through the so-called “consular processing”, which means by filing for an immigrant visa with a US consulate abroad.
Form I-485 is a complex application which usually requires filing of additional complementary USCIS forms and supporting documents. If you have any doubts as to the filing process in your particular case, you should consult an immigration attorney.