After your bio is approved and is moved to the approved section, it's absolutely forbidden to edit it. Besides after a while you loose the ability to edit your posts.
If you want to add the new stuff you learned you post the bio again, just like the first time, in the biographies section, only this time with the new stuff and you wait again for approval. However don't start updating your bio for every single thing. If you have just gained one rank it isn't worth over to make an update. Most people wait -or should wait- around two months or so to update their bio. Only update your bio if you have a lot of stuff to add, so don't update it every single week.
When you update your bio you can change things, you can change things in your history so that they fit the requirements for certain skills etc. however wood can only be used by Shodaime, Yamato and Danzou bio's.
