I could not find in my online application form any methods to upload my documents.

You could only upload documents to the online system after submission of your online application form. In other words, it is normal that you do not see a field for uploading documents when filling out the application form, but only after submission. All supporting documents, including reference letters and curriculum vitae, should be uploaded to the online system within 4 weeks after the creation of your account, or by the deadline of the clearing round, whichever is earlier. You would not be able to upload any documents to the system afterwards.

Please upload all your supporting documents at Application for Taught Postgraduate Admission after logging/re-logging in with your username and password.