Fixing bath/shower mixer tap

Hi

Hoping someone can help!

The mixer tap in my bathroom stopped working about a year ago. It was never really a pressing repair so it got sidelined: now doing the house up to sell so I figure I best get it fixed.
Essentially, water comes through the shower heads but not the taps. The toggle that went up and down to change between the two outlets no longer works.
From what I've read, I need a replacement part (although what it's called I don't know) and I need to switch the water off, remove the part and replace.
Can anyone tell me what the part I need is called and the tools I'll need to do the job. I'm a DIY novice so I'd rather know if I'm taking on more than I should before I de story the bathroom and the job ends up costing more than it would have to get someone out to fix it.
I've attracted pictures to give a rough idea of the tap unit.
Thanks fle

this type of tap has a spring inside,what I do is remove the spring and then you will have to lift it up to open and push it down to close,

As long as the taps are off there's no need to turn anything else off.

There should be flat section on the diverter which will enable you to unscrew (anti-clockwise looking from above). You will be able to lift the diverter assembly out of the tap. Probably needs replacement 'O' rings - take the complete assembly to a decent independent plumber's merchant and see if they can help you out with replacements.

Thanks! Will try taking it apart at the weekend and will take it from there.