1) Are you absolutely positively sure it's not load bearing? 2) You will need to check you don't need some sort of beam/RSJ to support the ceiling when you take the wall down 3) What is the wall built of? If brick.block built they can be surprisingly hard to take down, even with a sledgehammer, unless you've a nice Strong Man to hand.
Yes, it's not loadbearing, just a celing/flat roof above it. DP's quite strong. He could probably do most of the heavy work. I'm planning on cutting a sort of square arch out of it but not sure the bricks across the top won't fall down.
Just because it's only got a flat roof above doesn't mean it's not loadbearing. The wall may be supporting short joists in that roof - it's really strange to build a non-load-bearing wall from bricks. Be careful.
You need to get a proper professional to look at it. It may not APPEAR load-bearing but if it is a flat roof about it is more complicated that you think, especially if that floor roof is concrete. An engineer will do the calculations you need. If you want an arch/squared bit then you will need a steel joist to hold it up.
On the bright side, lots of housebuilders are laying off people so you should be able to find someone to do it...
don;t do it......not without advice first from a builder.
a friend tried this, without asking my DH (who is a builder/bricklayer), and the ceiling fell down! she was lucky, hers was in an extension with a flat roof above, so it did not cause a room to cave down, but it left her with major leak which they only discovered after a hugely heavy rainfall and their entire downstairs was flooded and ruined!