There are two possible approaches to upgrading a stack to the latest version:
The first, simplest option is to create a new stack in the latest available version and then set up your data feeds to use the new stack before deleting the old stack.
The second option is to request an in-place upgrade to the latest version where the existing stack ID is retained and the data is migrated by Logit into the upgraded stack.
With the first option, because it is a brand new stack, there is no need to migrate data and therefore no risk of data loss. With the second option, there is a very low risk of data loss (we haven't had any cases of data loss to date) but we can't 100% guarantee data will be restored back into your Elasticsearch cluster.