1. On the ITC 2019 website (https://www.itc2019.org), you need to log in first and go to the Validation page.
2. Here, you need to validate your solution first (choose the solution XML file and click the Validate button). The page may take a bit of time to respond as it needs to upload the XML file and validate it. Please note that the file needs to be in the solution XML format with the instance name matching the name of the instance for which the solution was created.
3. If all goes well and the solution is valid (all classes are assigned and there was no issue was found with student class enrollments), the Upload solution form appears below the solution properties. The parameters are pre-populated with the data from the XML file, so all you need to do is to hit the Upload button and you should get a confirmation afterward (you can also change the solution parameters here or later on the My solutions page).
4. Now you can continue with the next solution (by choosing a file and hitting the Validate button again). Also, you should see your uploaded solutions on the My solutions page.