iPhone 4 help

So, my mother's iPhone 4 is all the time not working and it's really buggy and slow due to iOS 7. It had a lot less problems when it'd iOS 6. So i was wondering if there is any way to downgrade to iOS 6. Note- I have not saved the ShSh blobs and I'm running osx so ifaith won't work with me. So how do i downgrade??