The updates are available for three models: the DMR-BS850, DMR-BS750 and DMR-XS350. Click on this link to go directly to the relevant download.
Failing that, there should be an 'over the air' update sometime today; just make sure you have the option set within the settings menu to 'automatically download'.
The only remaining Panasonic products without BBC iPlayer compatibility are the firm's 2008/2009 TV sets. Panasonic says the upgrade for these will now be available in September 2011.