Our system detects the new version, automatically our pipeline works to package, compile, test, etc the new version, if everything works fine, the release is launched and published in the cloud providers. If it is a new version with a lot of changes or the automatic process fails, we work on it manually according to different priorities and SLA. This process publish new versions, but current stacks are not affected.
Bitnami stacks don't include any auto-update tool, so your stack is a "closed system". You need to upgrade it manually or launch an instance with the new version and after that migrate your current data to the new one. So you can rest assured that your stack will not update automatically.
Carlos R. Hernández