You can remove the passcode by restoring your device from iTunes or Find My iPhone if you've turned it on before. The catch here is that you will lose your data by following the above method, so you should be aware of that. If you don't want any data loss, then you should first enter into DFU mode and use apps to get the passcode and paste the code somewhere, then exit DFU mode and input the passcode you just received. This method was recommended by a friend of a local workshop. More details can be found here, and you can leave comments for further requests.