I need to change the chainset on my carrera vengance 27.5 frame and wheels What chainset would you recommend for my bike I'm new to cycling and pretty well I'm a virgin tbh,,,it's 24 speed carrera vengeance the one I have now well it looks like it's warped when peddling,It also slips whenever I put real pressure on it I smashed my knee last time on it...it also makes the chain hit the gear selector for the big cogs.thanks...
Have someone look at the crank. As mentioned in comments the whole crank may not need to be replaced.

If the crank does not replacement: The Halfords web page for the current Vengance model shows the bike has a mix of Shimano Altus and Tourney components, a Suntour XCE crank and a square taper cartridge bottom bracket.

Assuming your bike is the same, you can actually replace the crank with any square taper, triple ring crank designed for 8 rear gears, with the same chainring sizes (42/34/24 for the current model, but check what you have). 

There are a number of manufacturers that make inexpensive cranks, a replacement Suntour or Shimano Altus crank are safe bets.

The Suntour XCE crank appears to have removable chainrings so if your big ring is damaged you will be able to replace it. Many inexpensive cranks are riveted together and the chainrings are not removable.