Not sure what I'm doing wrong here.. I'm new to 5e and the last time I played any DnD was the version 3 rules I think.

Anyway when i go into the spellbook using "K" I can unselect a spell but I cannot select another one to replace it.. nothing happens. Still have 5 out of 6 spell slots.

What am I doing wrong? Resting doesn't do anything, I tried selecting spells in camp or town and nothing.

Advise? I have tried to find this by searching but nothing so far.

Could be that I'm just a complete noob again and doing something obviously wrong.

Thanks guys!