Tom is referring to your Construct license.
So if your using a C2 Personal (5000$ US Profit Limit), C2 Business Edition or a C3 License (except educational) go WILD and have fun.
[quote:1g7fbva3]How much should it be changed, such that to not be accused of copyright problems? Thank you!
It's up to you, but being Royalty free, you don't need to change anything. But if you want to make money, you may want to change the graphics.