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 Keyword Ideas page, which you do via the following link:
Then once you've landed on this page, you'll see a basket with your chosen keywords next to the yellow button with an arrow:
Once you open the basket you will see all of your chosen keywords. Simply press the red '-' button next to the keyword you want to remove and then click 'Save Keywords':
Second option - you need to navigate to Keywords page, which you do via the following link:
Then, you need to click on the gear icon, like below:
Then you can delete keywords on the following page.