There is no in-game way of removing learned spells, but if you're playing on PC you can use the Spell Eraser mod.
Adds a power that removes spells from your character.
Some spells become obsolete as part of your character's progression. It's by design. It helps, then, to have a tool to remove these clutter spells from your magic menu when you no longer need them. Spell Eraser is such a tool. It also helps with leftover spells like "Arniel's Convection" after their quests are over.
Equip the Remove Spell power and the spell you want to remove, then just cast the power and hey presto! The spell is gone. You can also remove two spells at a time by equipping one in each hand. Note that some spells (like your starting Flames and Healing) cannot be removed.