Many Steinberg products are available as a crossgrade at discounted prices. To crossgrade means to switch from a specific software to another.
For example from Cubase to Nuendo or from a 3rd party program to Steinberg software. Among others, it is possible to change from Live, Logic Pro, Pro Tools, Sonar, Fruity Loops, Digital Performer, Studio One Professional or Reason to Cubase - or from Sibelius or Finale to Dorico.
A crossgrade requires that you own the corresponding software license. Crossgrade offers do not embrace rental licenses or subscription models.
Last, but not least: You may keep the license of the software your are crossgrading from!