Hi Pedro,
Well, technically speaking, Debug and Release are just two project configurations, which essentially differ for two things: the debug level (the Debug one is compiled with the -g3 options that adds more debug “information” to the binary) and the optimization level. But both of the two can be flashed on the MCU using OpenOCD.
When you compile the project, you should find inside both the Debug and Release folders a file named “.elf“: that one is the file to flash on the MCU using OpenOCD or other flash utility tools.
About texane and QSTlink2. They essentially do the same think, but I decided to talk about QSTLink in Linux because it also has a GUI that simplifies flashing procedure. However, OpenOCD is the only tool you need at the end.