Go to Cog > Administration overview
Go to Seminars > Event defaults > Custom fields

Click on the Sign up tab
Click on the Cog under edit
You'll then be presented with this screen:

Click into the Full name field and edit the text as required.
Go to Cog > Administration overview
Go to Seminars > Event defaults > Custom fields

Click on the Sign up tab
Click on the Cog under edit
You'll then be presented with this screen:

Click into the Full name field and edit the text as required.