If you've chosen a keyword that you now want to remove, then you have two options to do this.
First option - you need to navigate to the Keyword Ideas page, which you do via the following link:
Then once you've landed on this page, click this button to view your chosen keywords:
You will see all of your chosen keywords. Simply press the red '-' button next to the keyword you want to remove & click 'Next'.
Check the changes to your chosen keywords & click 'Save'.
Second option - you need to navigate to the Keywords page, which you do via the following link:
Then, you need to click on the 'Settings' (manage keywords) icon, like below:
Then you can delete keywords on the following page.