Editing h1 tag

On our website (http://www.northamptoncomputerservices.co.uk) we have two H1 tags on our homepage. We’d like to know which file we need to edit in order to change this part of our homepage as we cannot figure out which file this part of the code seems to be in. We’d be so grateful if someone could go on our site, check out the source and hopefully let us know how to edit the H1s.
Thank you