Upgrade path : DDOS 6.2.0.20 to latest version

The latest DDOS version is 7.8.x

Unfortunately, as I only use DDVE, I cannot tell you about the specific upgrade path for your DD. You may find some information here: https://elabnavigator.dell.com/eln/components

May I suggest that you better ask support, especially for discontinued hardware.

Having access to the Dell https://www.dell.com/support is pretty much mandatory, not only for getting the rpm's but also to sift through the mandatory documentation to get to know what to do?

From the "Dell EMC DDOS, PowerProtect DD Virtual Edition (DDVE), and PowerProtect DD Management Center (DDMC) 7.8.0.0 Release Notes":

"Update to 7.8.0.0 using the UI is only possible from the following releases: 6.0.2.70, 6.1.2.70, 6.2.1.x, 7.0.0.20, 7.1.0.20, 7.2.x,7.3.x, 7.4.x, 7.5.x, and 7.6.x. Other releases must download the corresponding MDU bundle from the http://www.dell.com/support site before upgrading to 7.8.0.0 in one hop, and follow the update instructions as described in Updating to DDOS version 7.8.0.0."

So if you are indeed running 6.2.0 then you'd require a MDU first and then you could upgrade to ddos7.8.

But beware that up until recently DDOS7.2 was the target release, none of the more recent versions. Now with DDOS7.7 they made that a LTR release. Depending on how you actually use the DD, also dtermines whether or not you should even upgrade at all. For example when using it together with Networker, if the DDOS versions is too high and the NW client version too low, then it might not be only unsupported, but clients might not even be able to use client direct with dbboost and write directly to the DD in question!

So you'd have to check in-depth, what systems are using the DD and what DDOS version they support. We've been stuck between a rock and a hard place in the past where we had to upgrade both the NW servers and DDOS in one go to have them supported again, taking for granted that various older NW clients (mainly due to old, unsupported OS'es) no longer would be able to directly write to the DD. This can all be checked and verified and guesstimated in advance, all determined by how you use the DD.