although it is a newer version, the old instructions are still valid, the only difference is the access point.
usually when file upload is not working it is because you are manually changing the type of the form element from text to file. when you do this manually, it will not change the encoding type of the form.
In the tag selector, select the form tag, then in the property inspector, make sure to change the encoding type to multipart/form-data
if you continue to have a problem, send a copy of your page so I can look at the code.