Change of Status vs. Adjustment of Status
Change of StatusGenerally when non USC's come to the United States, they usually come on a visa. Noramlly, they enter the US on a non-immigrant visa. Sometimes while the person is here, they want to stay longer and they can request an extension of status. If a person let's say enters on a visitor's visa but then is offered a position, they can apply for a change of status to an H1-B or if they choose to go to school, they can apply for a change of status to a F-1, M or even a J visa. However, in order to do a change of status, the person must be in another valid non-immigrant status.
Adjustment of StatusThis applies while an immigrant is in the United States and wants to adjust status to that of a lawful permanent resident. Again, this person MUST BE in valid non-immigrant status. There are some exceptions such as an immediate relative or protection under 245(i). Nevertheless, the person applying for adjustment of status needs a basis such as an family based immigrant visa (I-130) or employment based immigrant visa. (I-140).