While you can only select five (5) courses to display on your KA dashboard, you can take and complete as many KA courses as you like.  On your Learner Home Screen, you can click the "Edit Courses" button (on the right, below your badges and above the first row of courses) and select different courses or you can click "Courses" (in the upper-left corner, above your avatar and to the left of the search box) and select any KA course.