how can I transfer by bluetooth Iphone to windows PC?

Using iTunes not Bluetooth > Import photos and videos from your iPhone, iPad, or iPod touch to your Mac or Windows PC - Apple Support

You cannot, file transfer is not supported over bluetooth ,although there may be Apps that can ,look in the App Store

or,You would have to use a third party wifi solution

You'll need a third party App to do that. The iPhone cannot natively share files over bluetooth with a computer.

This one has good reviews:

https://itunes.apple.com/us/app/supershare-lite/id427543889?mt=8

No direct Bluetooth connection to PC. If you just have one or two photos email them to yourself so you can download them on the PC. If you have many then install iTunes on your PC and sync them that way.