Given the existence of the statehood movement in Puerto Rico, what would need to happen for Puerto Rico to be the 51st State of the U.S.A.?
After their last hurricane, how would the help from the US have differed had Puerto Rico been a state?
Bonus question: how do you arrange 51 stars evenly?
Puerto Rico would officially ask to become a state (customary but not explicitly constitutionally required). Congress could pass a law admitting it as a state. You can read more about that here, which was previously posted in a comment.
It's unclear how this would have changed aid. In theory, states have more influence on the political process than do territories, as the state would have at least one Representative (probably four for Puerto Rico) in the House plus two Senators. In practice, Puerto Rico is overwhelmingly Democrat, so they would have little influence on the Republicans who control the presidency and both chambers of Congress. So the answer might be no change at all.
It is difficult to give a definitive answer though. We can only speculate on the changes that that would make. A lot would depend on how effective Puerto Rico's political representation was at influencing the government. For example, might they appoint a Republican Senator to represent them so as to have more influence?
Adding two Democrats to the current Senate would create a 51-51 tie to be broken by Vice President Mike Pence. Republicans would not be able to lose a single member of their caucus. John McCain's illness would leave the Republicans effectively down 51-50. Of course, that might increase the pressure on him to resign so that Arizona could appoint a replacement.
We can go round and round with that speculation. It might make a difference or not. We can't do it both ways so as to compare.
Bonus question: How do you arrange 51 Stars evenly?
This has six rows alternating nine and eight stars per row. This contrasts with the current flag, which has nine rows. The first has six stars, and it alternates with five stars thereafter.
3 * (9 + 8) = 51 5 * 6 + 4 * 5 = 50
There are other potential designs on the Wikipedia page, but this seems the most likely. It looks the most like the other flag versions.
The official flag design has been set by executive order of the president since 1912 (by custom). So the actual design chosen might depend on which the (then current) president likes best.
@Brythan is correct in terms of the practical process that would likely be followed. Constitutionally, there is a specific requirement:
New States may be admitted by the Congress into this Union; but no new States shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or Parts of States, without the Consent of the Legislatures of the States concerned as well as of the Congress.
As no part of Puerto Rico is "within the Jurisdiction of any other State", and admitting it would not form an interstate "Junction" (unless, for example, some Congressional representative were to try to sneak in a merger of Florida and Georgia along with Puerto Rico as some sort of State of Peach Sunshine Caribbeania), no state legislature approval is required. All that would be required would be for Congress to approve Puerto Rico's admission.