Prestashop set customer id in context and use it without refreshing the page

I have this issue with Prestashop 1.5.4 who uses the context object.

I'm creating a custom one page checkout with Ajax.

When the customers input is validated I insert this in the related database tables and receive the customer id. So when the customer changes some things I don't wanna insert it again but update his data. But I don't know how I can do with the context object.

I want something like this in my controller:

if (!$this->context->customer->id){
// there is no data of this customer, so insert it in the database

// set customer id context
}
else{
// there is data so update it
}

I tried a lot of things like:

$this->updateContext($customer);

$this->context->customer->id = (int)$customer->id;

$this->context->customer->update();

etc. etc.

Who can explain how I can update the context without refreshing the page?