In ToB, I=My mage,Imoen, had some spells memorized in her spellbook which I would like to erase so that I can learn some better ones.
For example, the third level spell, mass invisibility which I could use to replace clairvoyance, which I have never used to this point. Since Imoen is allowed a finite number of spells per level, how can I , if I can, erase one spell to make room for another, unlearned spell?
I tried drinking a potion of Insight or genius, but that did notwork, nor does changing a ring or a ioun stone which , the description says, allow me , (Imoen) to learn another level spell slot/
Hope I made myself clear in this question.
Thanks for help.
Muzzien

Just open the spellbook and click on one of the spell slots that has a spell in it; that will remove the spell from the memorization slot so you can pick a new spell to memorize.

Note that you will need to rest before you can actually cast your newly memorized spell.

Edit: If you want to delete the spell from a spellbook entirely, try right-clicking on it.

Open her spell book, right click on the spell you wish to remove and select 'Delete'.

The extra spell slot the description mentions means that you can cast another spell of that level, not that you can learn another spell of that level. You can use an extra spell per day, not add an extra spell to your spell book.

so then: if I wanted to remove . say, a level three spell , in my example, Clairvoyance,from those memorized in my spellbook and replace it with another , more useful level three spell, say invisibility 10 foot radius, which I have not yet memorized, I could not do it, even if my spellbook is no longer at capacity? I am stuck until Imoen levels up and gets another level 3 spell slot open?

I appreciate the responses from the community.

First, you need to answer an important question: Are you trying to change the spells that are in your spell book (the spells that your wizard can choose from when memorizing spells), or are you trying to change the spells that are in your spell slots (the spells that you actually want to make ready to cast after you rest)?

If you want to change the spells in your spell slots, then left click on the spell slot holding the spell you want to remove. If it is actively memorized, then you'll get a warning message that you're about to remove that spell from memory (so you won't be able to cast it until you rememorize it and rest). That will empty a spell slot of the relevant level. Then just left click on the spell in your spell book that you want to put in an empty spell slot.

If you want to add a new spell to your spell book, but your spell book is full, then you need to remove a spell from your spell book (meaning you won't be able to memorize that spell for resting). Right click on the spell in your spell book, get the warning message, and confirm that you want to remove the spell from your spell book. Then have your wizard right click a scroll of the new spell and write the new spell to your spell book (don't just cast the spell from the scroll!).

I told you what to do.