How do I change the pressure on my combi boiler, and how to turn down the w?

my boiler is an Ideal mini C24...the pressure is very low and the hot water is coming out unbearably hot even tho i have turned it right down, and i don't seem to be able to add any cold to it...the two don't seem to come thru my bath tap at the same time. I'm skint and can't afford to have a plumber come and look at it. Please help!