I am wondering two things about replacing a font in the shared font library:
What are the steps to replace a shared font that we are currently using in our organization with a new version? For example, we are currently using v1.001 of our brand font that is in our shared font library and we want to replace that font with v1.003 which has slightly different characteristics. Do we have to remove the old font and upload the new font?
After the new font has been uploaded, do we have to go into our libraries and replace the text styles for shared components with the new font manually, component by component?
For the first question, you can upload the new font without deleting the old one; however, if the new font uploaded has the same family name, you select “replace” to update the existing font with the new one (I believe this also removes the need to do the steps described in my next answer).
For your second question, I would recommend going in to the library where you created your type style, update it to use your new typeface, and re-publish the library. As long as all your components are referencing the same type styles from one library, you will not need to update component by component. If some components are not referencing a type style, you will need to manually update in each one, but the Font Replacer plugin might help speed this up.
If you changed your type styles from Avenir to Calibri, you can either manually change it back, or, I believe you just need to go back in version history to when it was Avenir, restore, then publish the library updates.