Without seeing it it is harder to comment but my usual technique if the substrate will stand up to it without damage is a few swift blows to start with a heavy hammer to shatter it, as cement tends to be hard it will fracture. However it still will require a reasonable amount of pry bar work to tease it off. But do monitor the background if you do this as you dont want to damage it.
As Jon says, it all depends on how the cement render was applied, and on to what.
If (as is probable) it's on EML, then - in my limited experience - you might be lucky and find that the nails securing the EML to the timberframe have rusted a fair bit. If so, then once you've hacked your way through the render into a cavity, you may find that, armed with a wrecking bar, a hard-hat and a tough pair of work gloves, you can actually rip off a considerable amount of the render/EML sandwich, working your way from stud to stud.
Be careful, though. I was doing this once when a rather larger-than-planned chunk decided to detach itself and descend on top of me.
Cement 1 - Penners nil.
If you think this could happen, use an angle-grinder to cut the stuff into bit-size chunks before you start heaving it off.
My advice would be similar to the ones above.
I wouldn't hit it with hammer to shatter it mind.
I would make and indent to the cement, just to the side of the lintel, and then gently tap a bolster inbetween the cement and lintel, watching carefully that the lintel isn't crumbling away, or dropping down.