O.k then I`ll start by saying that your tv just replicates /displays whatever picture is sent to it as a set resolution determined by the equipment sending it (freesat box in this case) and at up to 1080p/60p (frames)
That is the maximum resolution at this point for standard video equipment .
But again ,, the tv does not set the resolution it merely display what is sent to it , it is just a monitor and if the resolution can be changed then it will be at the equipment that sends it .
Usually you can lower the resolution but by default equipment like blueray ,cable box, satellite receiver etc. will send the picture to the max. resolution it can .
The option to lower the resolution is usually there so that equipment will be compatible with older TV's but again it has to be manually lowered as it runs at top speed if you will by default .
So , if the problem persists then the solution is at the freeview box and perhaps I could help you with it if you could give me the model number of that box.
I also noted that you said hdmi/dvi , does that mean that you go from hdmi to dvi at the tv ?
How old is this tv ?