By these recommendations, we concentrate on a limited number of upgrade steps that are used by the vast majority of users. Thus, if a bug appears there, it is likely to be reported and fixed; thus, further bugs in these limited upgrade combinations get rare.
Software
First, update to the latest patch release of your current major version, e.g. v1.6.0p2 → v1.6.0p30. Then, take the latest patch release of the next major version, e.g. v1.6.0p30 → v2.0.0p36. Then again latest patch release of the next major version until you get to the current version and its latest patch release, e.g., as of the time writing this, v2.0.0p36 → v2.1.0p28 → v2.2.0p7.
Take all intermediate major releases within the upgrade.
Firmware
Same as for software, first the latest minor version, then the latest minor version of the next major version, and so on. E.g. v1.3.20 → v1.4.19 → v1.5.5 → v1.6.4 .
You need to take care of the availability of the software for each firmware version.
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