The number of simultaneous downloads can be increased by visiting the Transfer tab inside the program's Control panel. I have installed the application and customized the settings to show you how you can achieve maximum downloads. The speed depends entirely on your Internet provider and on your Internet subscription. There is no way to boost it above its limits.
A suggestion would be to disable the filtering on your computer (firewall). Go to
Start > Control panel > Security Center> Windows Firewall > Turn of Windows Firewall.
I have attached an image where you can see where you need to modify the settings for maximum number of downloads.