How much of my work do I have to change if similar to someone else's work?
There's a myth that US law states if you change a certain percentage of someone else's work, you will be able to claim a copyright in that work. This is not entirely true. Only the owner of the copyright in a work has the right to prepare, or to authorize someone else to create, a new version of that work. Accordingly, without the owner's consent you cannot claim copyright to another's work, no matter how much you change it.