how easy is it to sack your solicitor in the middle of a case?

[drxerox]

a friend had an accident a year ago and still suffers from the effects of it. The solicitor they chose, a year ago, appears not to have expertise in the area of head injuries and hasn't been as proactive as they should have been. for example, they still haven't obtained an interim payment, almost 2 years on, when the other party has admitted liability.
They would be paid from the final payout. Is it possible to change solicitors at this juncture?

Yes you can change if you are not satisfied with the service you are getting.
You can approach another solicitor and ask them if they are willing to take the case on (you will need to shop around to find one with suitable experience in the accident field).
Then contact the current solicitor and give them the name and contact details of the new solicitor.
They will not release any paperwork though until you have paid their bill in full so the case wont progress any further until that is sorted out.
You possibly wont be able to claim for the original solicitors fees out of the compensation so this will be 'lost' money but you may get it sorted a bit quicker.
I waited over 2 years for my case to go to court and be agreed due to the insurance company wanting all sorts of odd things from me before they would make a decision on a settlement. These things do tend to drag on.

In answer to the OP's question - easy.

Just write them a letter telling them you will not be using them again, asking them for their final invoice and collect your files.

If it's in the middle of the case I'd recommend making sure you go and collect the file rather than waiting for it to happen.