Can a plaintiff amend his complaint to state a different cause of action?

Moreover, "[c]ontrary to longstanding rules generally precluding a party from changing the theory of the case on appeal [citations], a plaintiff may propose new facts or theories to show the complaint can be amended to state a cause of action, thereby showing the trial court 'abused its discretion' ( 472c, subd. (a)) in not granting leave to amend. The plaintiff 'must show in what manner he can amend his complaint and how that amendment will change the legal effect of his pleading.' [Citations.]" (Connerly v. State of California (2014) 229 Cal.App.4th 457, 460, fn. omitted (Connerly).)