A lot of things can be done with the firmware of Synology already. But sometimes an additional feature is needed that isn't supplied with the firmware. The solution to this is called ipkg (Itsy Package Management System). This is a package management system for your DS, which allows you to install additional software.
The ipkg software is plattform dependent, so please first check which processor is used on your DS. Which proccessor is on my DS?
Furthermore telnet or ssh access needs to be activated.
After that the installation file can be deleted