Hello Giedre,
1. You should go to the back-end of your site, then go to EShop -> System -> Configuration -> Option tab, at "Allow Ask Question", choose No to hide Ask question button on the product page.
2. If you want to change label of that button, simply go to EShop -> System -> Translation, then filter the language item "ESHOP_ASK_QUESTION" to edit and change it as the way that you want.
3. To edit the subject and content of the email of that form, you should go to EShop -> System -> Messages, then look at "Ask Question Notification Email" and "Ask Question Notification Email Subject" to edit them as the way that you want.
Hope that my answer are useful.
If you need any other helps, please go to our ticket system at
www.joomdonation.com/support-tickets.html
to submit new ticket there so we can help.
Sincerely, Giang