[College Trigonometry] Graphing Sin/Cos

When Graphing y=sinx I understand most of it but when I come across problems like this for example Y=4sin(x/2+pi/2)-2 the Instructor told us to take out the "x/2" first so then we can have our b. The problem would now look like this: Y=4sin1/6(x+pi/3)-2 I know how to graph it from there but I have a problem of understanding how to take out the x/2 and making the x by itself. Im not sure how pi/2 became pi/3 etc I dont understand what he did here.