Update,

no new citation

e.g. no change to conclusions or authors

Update,

requires new citation,
conclusions not changed

e.g. includes change in authors

Update,

requires new citation, conclusions changed

e.g. now sufficient evidence of an effect

Amendment, requires new citation, conclusions changed

i.e. correcting a serious error in conclusions (Erratum)

Amendment, requires new citation, conclusions not changed

i.e. correcting a serious error in citation (Erratum)

Amendment,
no new citation e.g. correcting a minor error, or changing methods