Q: I need to deactivate find my iphone tu install iOs again, but I can't connect with wifi

sorry dont know the solution but have seen this issue alot with iphone 4s when user update it with 8.3 if u can downgrade its better. Try to download the ipsw for your iphone model and install it using itunes through cable thats the only solution.

kunalsinghbhati,

Apple does not support downgrading the iOS. Your suggestion to the OP is worthless.

SUHELIS,

Did you try the step shown at this link?

If Wi-Fi is grayed out or dim on your iPhone, iPad, or iPod touch - Apple Support

If so and it didn't work your next step is to contact Apple Support. There is a Contact Us link at the bottom of this page.

Since no one actually gave you a helpful answer...

1. Go to iCloud.com on a computer and sign in with your apple ID and password.

2. Click on find my iPhone

3. Click All devices (Top middle)

4. Click on the device you want to remove.

5. Click remove from account

OR

Put device in recovery mode and restore through iTunes.

Then activate the phone using your computer if the wi-fi still doesn't work.