Hello,
Maybe someone can help me.
I've send my siacoins from the wallet to bittrex. The problem is that it remains unconfirmed.
I think i have done something wrong. But maybe someone can tell me because i dont know what to do.

You will help me a lot!
The transactions go from unconfirmed to confirmed in the Sia UI after being included in a block. Blocks are generated on average every 10 minutes, but sometimes a block can take 30 minutes or more (in the same sense, it can take as few as a few seconds).
You can check if the transaction has been included in a block by pasting the hash of the TX on the "hash" field of Sia's Explorer:
http://explore.sia.tech/ Once included in a block, the particular policies of each exchange may make your funds not being available after a number of extra blocks (comfirmations). Generally, it will be credited after 6 blocks (one hour).
Probably by now your transaction has been already credited by Bittrex