TRanslating a theme, simple question

Hi folks, I’m new to wordpress, my version of WP is in spanish and theme is in english so I want to translate it.

I’ve tried with a localization plugin but aparently my PHP version is too old because it does not work.

I’m not a pro so this is what I wanted to do: open every php file on my pc in dreamweaver and translating directly english sentences (in html) to spanish and then uploading the theme again.

Is that OK?