My knee-jerk reaction is that you should just use iron-router. However, that may only make sense if you are swapping out templates based on routes. If you are sticking with the same route and only changing the partials then you can accomplish this with session variables.
When the user clicks the 'next' button you can set a session variable like:
Template.myTemplate.created = function() {
Session.setDefault('currentStep', 1);
};
Template.myTemplate.events({
'click #next': function() {
var step = Session.get('currentStep');
return Session.set('currentStep', step + 1);
}
});
Then you can add a helper like:
Template.myTemplate.helpers({
isStep: function(n) {
return Session.equals('currentStep', n);
}
});
Finally your template can select the proper partial based on the session:
<template name='myTemplate'>
{{#if isStep 1}}
{{> step_1_Template}}
{{/if}}
{{#if isStep 2}}
{{> step_2_Template}}
{{/if}}
</template>