Well... it is exactly what the title is saying.
 
I'm having troubles upgrading my attributes. 
 
Courage, academic and charm
 
Where can I upgrade them outside of the school?

go the karaoke place in the mall at night.

Oh man. I've been playing too much portable. On FES you have your desk in your room that you can study at. That will give you academics. Also, after school you can study in the library by the faculty office. Also, there's the option of going to the diner by Hagakure. I forget the name, but they have this meal that raises your academics. The karaoke bar and Wild Duck will give you courage. You can get a charm boost by going to Changall. Their coffee makes you more charming. The trick with them is to kinda just get them all out of the way early on so you can get to enjoying yourself. Especially if your interested in pursuing a social link with Yukari or Mitsuru. Also, just a quick plug, but the PSP version makes raising your attributes a whole lot easier. Anyway, hope that helped and good luck buddy!

A good way to do this without dedicating any actual time out of a day is to make sure you visit the nurse's office whenever you are tired or ill, you will get the option to take a strange drink which increases courage.
 
You shouldn't really have to waste any time increasing any of your stats as you will always end up with some free windows to do that in, only do the activities to raise stats if no S-Links are available. By the time the first S-Link was open to me that needed a high stat (like Fuuka) I had already maxed out my courage. It will quickly become a non-issue, Academics takes the longest but its a long time before you really need it.

" It will quickly become a non-issue, Academics takes the longest but its a long time before you really need it. "

" @WatanabeKazuma said:

" It will quickly become a non-issue, Academics takes the longest but its a long time before you really need it. "

IIRC, it was only really needed if you wanted the "top score" gifts from Mitsuru, and initiating her S-Link in the first place. "