Hello Prashant,
A little confusing.
- 5420 release version is v8.4
- 5520 release version is v8.2.5, so I suppose the question regards model 5520 and not 5420.
Since v 5.2.5 is the first release supporting 5520 models it is
NOT possible to downgrade to an earlier version than v8.2.5.
When it is required to have the same sw version on all VOSS switches, you can upgrade the others to v8.4.x.
regards
WillyHe