You first need to remove the "round thing" with the multiple holes. For that you need a spanner tool (red version) you can get at any bike shop such as Performance. If you try to remove the hex bolt first you will damage the crank. Once it is removed you can unscrew the main bolt with a hex key, then you pull the non-drive crank out as well as the washer. Then, assuming you have a mexa-exo bottom braket, use a rubber mallet to tap the axle and the drive-side crank out.
The whole process is a piece of cake and should only take you about 5-10 minutes.