Yes, you should be able to do that. 31 days notice is required. Give Sky a call.
You don't say what package(s) you have but over £100 is potentially a lot... Are you 'out of contract'?
If so, you may be able to reduce the overall charge but agreeing a new 24 month term. (But remember prices will still increase annually)
@RogtheDodge24 wrote:
Can I take off HD?
Maybe consider what percentage of content you consume on Free To Air HD channels compared to the subscription output. Remember that upscaled SD can be pretty grim, particularly on a larger screen: might be worth trying a few now to see if it's going to be tolerable.