Hi,
2020 & 2040 share the same chassis, so technically it is doable to remove 2020 controller & slot in two 2040 controllers.
Having said this, licenses are not transferable, so effectively it is a new purchase anyway (NetApp normally offers some credits for the old system as a form of a buy back).
Personally I'd ask for a quote for a new spanking 2040HA, mentioning 2020 is going to be returned.
Regards,
Radek