You can use a screwdriver usually to remove them. Some are like thumbscrews where you can just unscrew them with your hand. If you need 6 standoffs, unscrew the ones you don't need.
You don't want standoffs where they shouldn't be, they will short out your mobo if you turn on your PC. You only want the standoffs in the holes with the silver/gold ring around them. The six standoff arrangement you said looks good, I counted the 6 too on a picture of that mobo. So only keep the "+" standoffs (+ and - are just a label for my drawing below) and remove the "-" ones.
+ + -
+ + -
+ +
- - -
The I/O part of the board should match up with the I/O shield in your case in the top left corner.