Number of Spells in Spellbook

[onemeg]

How do I increase the number of spells that my spellbook will hold? Right now I am level 5, and I have 4 scribed of each discipline. I recently came across Bless and Phantom, but it won't let me buy the scrolls saying there is no room. I went and sold off most of my scrolls thinking it would make room for them, but it still won't let me buy them.

Edit: I did some searching and see people saying that the spellbook holds unlimited spells and I don't understand this. I thought I kept seeing a tip saying to be careful because it's limited...Also again I sold off most of my scrolls but still cannot purchase. Any help would be appreciated :)