Downgrade Internet Service

Hello! I have seen a few helpful posts here where people have been able to downgrade their current service and figured I would post here to see if I could get some help!

I believe I currently have the 800mbps superfast plan, I originally went with this because I got a deal for a lower price my first year, this year has since ended and I would like to downgrade a tier to 400mbps if possible while still keeping my same equipment!

Thanks in advance!