Salesforce API connection changing

Hi. I need someone who can help me to fix the problem with the new form which included the upload file section too. The existing form without file upload. So the new form need to have a upload file section which will add the files to the Salesforce CRM. If the user already in the system the file just will assign to the user. But if not, will creating user with the info and uploaded file. That’s all. Thank you in advance.