How do I edit a script in FOMM?

[Bean0]

Well someone released a new weapon and I want to tweak it's .esp file.

So I got FOMM and I opened it up to where I can see the script of the weapon and I can see the lines of code that I have to change to get the changes I want. But I can't seem to be able to edit anything. I can highlight it, but that's about it but I can't delete or type anything in. Surely there's some way that I can edit the code, recompile it, and use it in the game. I just have no clue how.

 

And yeah. this is probably the most noobish thing ever, obviously the solution involves some program other than TESsnip but could someone tell me how to do it?