I found a iphone 5 how do i activate the phone using a different apple id?

I handed it in to the police and they said if no one claims it in 90 days it yours now it has been 3 months and the phone mine but i can't activate because i don't have the original apple id or password
the phone is running ios 7.
how do i activate it

You can't re-activate a lost or stolen iPhone, that's what Activation Lock is for. Basically, you have a very expensive brick that you might be able to sell for spare parts.

It's not possible to re-activate a lost iPhone thats what Activation lock's job is, however you can still sell its parts.