Configure and remove required fileds from the form (guest checkout and create new account)

[copymaker]

Hello everyone

I've in trouble with modifying the registration form in PrestaShop (instant checkout and create a new account). Because I absolutely don't know how PrestaShop works I need your help. 
Also, I've read all previous similar questions and answers but seems that it don't work for me that is why I'm writing here.  

I need to modify contact form for Instant and Create new account forms. 
I've made already some changes and that what I have for 'Instant checkout'

That's exactly what I need and the same for 'Create new account' but add a password field there. 
But when I click submit the form I get this (because previous form had a lot of required fields, that don't need right now)


And here is the question, how can I remove required fields for the form and is it possible to make at all?
I tried to modify authentication.tpl but It didn't help so I really need your help, I need to make this workable.