Right first off I am assuming this is a theme for a single person or business who wants to advertise their services in the 'building' trade or similar. If it's not aimed at that then it needs to be changed.
Ok... lets go page by page (desktop 1920x1080p resolution).
Home page:
It doesn't really tell me what the site is for
Lacks something punchy (image or something similar) to really pull me in
Doesn't need 'the gallery' section imo - I'd argue this might be more suited to the features page
Features page:
It's just a lot of text and then a contact form
See above that you might be better putting 'the gallery' from home page here because it's basically the same information by the looks of it
Not sure you need the contact form on the bottom of every page when you have the 'get a quote/contact us' box in the footer.
Download and Installation page:
Not sure this is something that needs to be in the menu up top - maybe look at the way some other sites, such as graphic river etc portray themes etc.
This type of image needs to be on the homepage imo, it's that sort of image that 'pulls you in' although in this case it doesn't fill the screen that well.
Testimonials page:
Honestly they mean absolutely nothing to me if they're on the site, so maybe look at linking in with one of the many review sites, either specifically aimed at tradespeople or companies in general.
Contact Form page:
As said it's a bit broken.
I'd also expand on the contact form itself, maybe break up what you'd expect in an enquiry into more individual boxes
Does it (or wordpress, I'm not overly familiar with it) come with all the scripting required for the form to function properly.... for me personally that is the most troublesome part of a contact form so if it's not included might want to include it.
General:
No location for a brand logo
I assume you can adjust the colours easily if they don't fit the company branding
I'm not sure the menu placement is right, could probably go top right considering how little there is.
As said, feels a little narrow, doesn't really make good use of the screen.