New website

We need a new WEBSITE. Unbeknown to us our current website turns out is a custom development. we have been informed by our SEO company that our text excludes keywords which we need to improve. Trying to upload some new text was an issue. The company that developed our web site now wants to charge us a lot of money to allow us to add text. see our website www.sfs-fire.com. Questions - have you created a website for a company that specializes in the maintenance and servicing of fire alarm systems?
We will need to keep the same URL'S.
We will ned a few extra landing pages and the format changed slightly.
We are trying to increase our google position so the new website needs to be responsive etc.
Could you answer the questions and give us a quote.
Looking forward to hearing back from you.