iphone 4s< update and find my iphone An iphone 4s at iOS 9.0.2 is asking to upgrade to iOS 9.1

The problem is that we know it's activation locked and we don't have control of that Apple ID.

Since I cant disable it if I can't remember a password. So if i update my iphone this will not block it or leave the phone bricked?

(The back story if it matters is problem when iphone was buyed from second hand user forget remove his accaunt, all was disabled but i make stupid thing i enable Find my iphone and now i cant nothing to do.)
If you update the phone, you might be prompted to reenter the password that you do not know. 

However, if the update goes bad due to file system corruption on the device you will not have the option to erase the device and start over. 

For that reason I would recommend not doing anything until you can get control of the device or you have a budget to replace it should you lose control of the secondhand and activation locked phone.