Browser upload can not be automated unless you use a test-tool. Take a look at SFTP/FTPS. Alternative is a Java application with http-client classes.
If you want to upload from Mendix consider calling a web service in a scheduled event.
If the file is from external system to Mendix: you'll have to write a custom java action to pick up files from a source location, read the binary contents and populate your Mendix object, and run this action in scheduled Mendix job.
If it's in other direction, exposing a web service is a good solution. Mendix uses a strange file naming system where files are inside numbered folders. In most cases, that won't suit you. Again, a custom java action will help.