Serum won't update

maybe i'm just dumb, but i've downloaded the serum update and it's still not updating. please help

You need to quit+restart your DAW. If Serum till shows as demo next time you start, most likely you have installed to a different location. Removing the demo plugin and verifying Serum is no longer available in the DAW would be the foolproof solution. See here if more info is desired:
https://www.xferrecords.com/serum/topics/if-serum-does-not-update-or-still-shows-as-demo

Let me know your DAW/OS if I can help further!

thanks, i appreciate it :)