A259 Lancing

From Old Salts Farm Road Lancing to Ropetackle Café in Shoreham by Sea my satnav says 40 mph.
This speed limit was changed to 30 mph in August 2016
I have a Kia Venga 4 ID B4E62AEFE031 My user ID is YN1179411163
The vehicle was registered in September 2017 – over a year after the speed limit change.
How can I get this updated as I am worried there may be other limit showing incorrectly on my system?
As it was a new vehicle I would have expected the information to be up to date.

it will be your sat nav maps that are out of date. as the road speed was changed in august 2016 that data would be sent to map company roughly in feb 2017 and then it can take upto a year to integrate into the new maps then it needs to be tested then released to the public so it probably will be on maps released early 2018.
Look for map updates for your system that are at least 2018 as they will be the most up to date, that data will be 2016/early 2017 data.
have a look at your satnav sytem data and it will show the map release date, post it here and i can tell you how recent it will be (remember release date on maps does not mean its latest stuff)