Legally-speaking I mean, not culturally. I know it would be politically unpopular.
Bear in mind I'm British, not American, so I'm not very familiar with the intricacies of American constitutional law. (We had the right to bear arms in the Bill of Rights in 1689, but we just changed it later like any other law)
There have been 27 ammendments to the US Constitution. The first 10 are the Bill of Rights and generally add to the Constitution rather than change it. Of the remaining 17, some add and some ammend but only 1 specifically modifies another amendment (the 21st repeals the 18th on prohibition). So the 2nd definitely could be amended, but just looking at the number of amendments it's not particularly surprising that it has not been.
Only the 18th Amendment has been repealed (Prohibition of Alcohol) by the 21st Amendment. The process for amending is complicated and after past by federal legislation must me ratified by individual states.