I posted my T5 earning in T4 now it won't let me change it?

You have to delete the T5 and then add the T4. If you are stuck on the T5 page, hit the back button at the bottom of the page.

To delete the T5, select Income>T-slips>T5 Investment Income and click delete next to the slip you no longer want.

To add the T4, select Income>T-slips>T4 Employment Income and click “Add T4 for [You Name]”.