I have a 2012 Cube LTD SL 29. xttp://mountain-bikes.gearsuite.com/l/4017/2012-Cube-LTD-SL-29

I need to make it faster. Could you suggest me a cheap alternative crankset? Do I have to change other parts as well?

I am considering the Shimano Ultegra Crankset FC-6800 2-speed 50/34 175mm
xttp://www.actionsports.de/en/shimano-ultegra-crankset-fc-6800-2-speed-50/34-175mm-3988 .

Would that fit my bike? Thank you all for taking the time to read about my problem and help!