I have not registered myself for jee advance then where I have to upload my ews certificate as I wrote jee mains with this category
As EWS category is started this year only , we can't say much about the process.
But as it just another category like the other ones , I guess the procedure will be the same.
For OBC , sc , St certificates , you don't have to upload the certificate anywhere but take it with you during the reporting after the counseling begins.
So I guess it is going to be the same for the EWS category.
All the best.
The Candidates of JEE (Main) January, 2019 as well as April 2019 Examination(s), who come under EWS category as per the Certificate issued by the Competent Authority, may mention such category in the Online Application Form available at www.jeemain.nic.in between March 11-15, 2019. The EWS Category Certificate is not to be uploaded in the JEE (Main) Portal. However, the same will be required at the time of filling up of the application for JEE (Advanced).
So according to this information, you have to post the certificates while filling up Advanced application form.
I hope this will help you out, for further query you can comment below.
All the best