If the council moves to four-year staggered terms, how should those be implemented?

That usually depends on whether the city uses at-large or district elections. If the city uses at large elections, the usual method is as follows: Assume a council with five members. At the first election after the effective date, those three (or two) members receiving the highest number of votes receive four-year terms, and the remaining members receive two-year terms. At the second election, two years later, those two-year seats are now open again, but this time the successful candidates receive four-year terms.

If the city uses some kind of district elections, the council usually prefers to designate which districts initially receive temporary two-year terms and which receive four-year terms; the designation usually is determined by lot or coin flip. (Any other method might be open to legal challenge.)