Hey there Suhail17,
Thanks for reaching out to Apple Support Communities. We understand that you're having some issues with your Wi-Fi speed after updating. We're happy to provide some assistance.
Does this occur with all networks or specific networks? If you haven't tested on another network, please do so to help isolate the issue.
Also, if you haven't already, try restarting both your device and your home network:
Restart your iPhone
If the issue persists after that, try removing the Wi-Fi network and re-joining:
How to forget a Wi-Fi network on your iPhone, iPad, iPod touch, or Mac
We hope this helps.
Have a great day!