Evaluting the method signature, it is required to know old password while changing it.
membershipUser.ChangePassword(userWrapper.OldPassword, userWrapper.Pas
Please note, all these mentioned solutions will only work if the RequiresQuestionAndAnswer property is set to false in Membership system configuration. If RequiresQuestionAndAnswer is true then the ResetPassword method needs to be passed the security answer, otherwise it will throw an exception.
In case you need RequiresQuestionAndAnswer set to true, you can use this workaround