Step 1 :
Go to CMS - System Management - Public Users - Select the authors which you want to add or remove
Step 2 :
On right top there is three dots (click on that)
Step 3 :
Under that you will find 2 options:-
1) Enable Show on Website and
2) Disable Show on Website
1) Click on Enable Show on Website - if you want to show that author on front end (Website).
2) Click on Disable Show on Website - if you don't want to show that author on front end (Website).