As Mike says you will need to go via version 6. As well as the release notes the following document details all the important points to consider when transitioning from 6.x to 7.x :
https://extranet.extremenetworks.com/downloads/Pages/dms.ashx?download=ca673e07-1e70-4997-9d18-66e71...
most important being :
- NāSeries modules must each have a minimum of 256MB of memory installed.Use the show system utilization storage command to determine the memory installed in each slot of your release 6.x system.
- N-Series firmware releases 7.11.x and greater utilize a new internal "binary" format for storing configurations. Versions 7.11.01.0025 or newer firmware will clear an internal configuration that was written in the older format. To avoid loss of configuration during an upgrade you must take specific steps to create and restore an ASCII configuration file. They are detailed in the document.
Best Regards
Glyn