I made a mistake and choose german againts English!!! Can I chance that? :(
If you mean that you want to learn German then yes, you can - in the settings. If on the other hand, you wish to learn English, then duolingo does not support that, AFAIK.
If your native language is Spanish and you want to learn English, then you can change that. Just move your mouse over "German" in the upper right corner and then click on "more". When the settings page appears, go to "Learning language", choose "Quiero apender Inglés..." and then click on "Save changes".
Your language should then switch to Spanish.