L4D Model editing trouble

I’m new to editing models with photoshop, I have the VTF file addon to photoshop but I can not open any l4d body model. It says I do not have enough memory(RAM) to open. My computer has plenty of RAM so does photoshop have it’s own RAM?
Important detail-Can not update past Photoshop v7 due to issues.

Can anyone tell me how and if this can be fixed?

Do you actually know what RAM is? Photoshop can’t have RAM unless they sent you a few sticks when you bought it.
You also can’t edit a model with Photoshop, so I don’t know what you’re on about.

Sorry, by edit a model I meant edit textures of the model.

What I do is open the vtf in VTFEdit and extract to tga

tga?

Sorry for the double post but could someone tell me what a TGA is and how to go about this process?