How do I edit my Models.dat file?

[RandomLoserGaming]

I have downloaded a few models, and it says to copy and paste something into the file. Problem is, I can't edit the models.dat file.
(I have the file with jims models, maybe that's why? Either way I still need to edit the file.)
(when I try to open it, it doesn't send me to notepad, it sends me to my browser.)

 

[SeventhSentinel]

Open Notepad first and open models.dat via its menu.

 

[Mathos]

Open Notepad first and open models.dat via its menu.

it can also be done by right clicking and clicking open with and the you choose notepad

 

[SeventhSentinel]

That's also a good way. .dat is an extension that isn't always readable in Notepad, though, so double check you don't set it as the default program by accident.