If you are using file manager widget than can change this in widget properties as displayed below. Please check your licence agreement to find out what is the maximum file storage limit for your cloud environments. If you are using Mendix Cloud V4 than you can check this by going to your environment details > General > Plan Details (see example screenshot below)
Hope this helps!
A regular file upload is not always the best option for very large files. It can be frustrating to wait for a file upload and then find that the connection was dropped and you need to restart.
You may want to look into ftp, a network share or services like wetransfer or dropbox.