You do not need to download a new client every time the server is updated. Simply go into the file where the client is, click update client, and wait for it to tell you that it is done and you can press any key to continue. MAKE SURE NOT TO [X] OUT OF THE UPDATING CLIENT AT ANY GIVEN MOMENT UNTIL IT IS DONE, OTHERWISE IT WILL MESS UP THE CLIENT AND YOU WILL HAVE TO RE-DOWNLOAD IT. I hope that answered your question.
If you have any other questions, please, feel free to ask them. Thank you,
Zelda.