1) Visit Admin > Structure > Profile Types to "edit" your signup forms.
2) On the profile edit form, note (or change) the custom URL path for that signup, e.g., "adult/register" or "youth/register" -- you'll enter this in a later step.
3) Visit the "Welcome" page at YOURSITE/en/welcome and click the "Edit" button (next to the "View" button, above the "Welcome" page title).
4) On the edit form for the Welcome page, describe each program and update the link if you changed it in step 2. Hint: put your cursor in the link you wish to edit, then click the little "chain" icon.
5) Scroll down and click "Save" -- then test the results.