There is a knowledge base article (which I have attached) that addresses the 1GbE to 10GbE process.
We did this upgrade last month. We first tried with v 2.0.8 of the Firmware but following the first controller upgrade the failover would not work (it failed the checks). We called support who recommended upgrading to 2.1.4
We did this but again the controller not fail over (which I don't see as an issue, as it was protecting me from failure). After a call to support, they immediately dialed in and did some diagnostics.. everything looked ok, so they did a manual fail over - all was good.
The support engineer had to log into the standby controller using private login credentials - this step is impossible for an end user or supplier, again something which would have been handy to know before we started the process.
Things to note, page 4 c) At the prompt, type halt --controller <standby controller>
This command wouldn't work... so I typed Halt --help
Unfortunately the array started an automatic shutdown and powered itself off. This needs addressing!
Ultimately the upgrade worked. It just took two nights of trying, which could have been expensive in terms of engineering time (it you are paying for it) and down time due to the Halt command. I was told that the auto checks look for the same number of NIC's (or the same IP addresses) before allowing the fail over - obviously going from 4 x 1Gb to 2 x 10Gb the NIC count is not the same. In reality this reason may not be true, but it fits the situation.
Hope this helps
Nick raises a good point here - only upgrade your NICs from 1Gb to 10Gb if you're on 1.4.x or 2.1.x firmware.
2.0.x has some inherent engineering complexities on live upgrading the NICs in the system, which was resolved in 2.1.
The Halt command was a CLI bug and as Rich mentioned is fixed in 2.2 which has just entered Release Candidate - but can also be found in 126.96.36.199 and above.