1) It may be possible to raise your memory limit, as in the thread that mbrsolution links to – add this to your wp-config.php file:
2) You could ask your web hosting company to either raise the limit, or justify it. There’s really no justification for it though – as I say, they’re easily in the bottom 1% there.
3) More technical is to go through your plugins one-by-one to find out which is the one using up most memory. Just because UpdraftPlus tips it over the limit doesn’t indicate that it’s the one using most memory – it just means that when UD gets its turn to run, it uses more memory than what’s left of the 40Mb; but “what’s left” at that stage could be anything. You can try disabling all your other plugins, and looking at the UpdraftPlus page, in the “expert” section (down the bottom) – there, it has a counter of memory used. Re-enable your plugins one-by-one and see which one causes the biggest increase in usage. I’d not really recommend spending huge amounts of time on that, though – it’d be more efficient to pursue 1) and 2) and if they won’t raise it for you, switch to a new web hosting company.