Don’t want to complicate things here, but if you passed your car test pre January 1997 then you might find the mod 2 and mod 4 route throws up a lot more complications than the 35 hours CPC.
In essence to do mod 2 (extended theory test) you need to book it online but if you passed a car test pre 97, DVSA / VOSA who run the tests have to confirm you’re allowed to do this by checking your licence with DVLA (utter totally stupid). However it can take them weeks to do this. In my case it was at least 2 months and lots of emails and phone calls before I could even book a date never mind do the test.
If you’re post 97 this isn’t an issue but you’ve also got to deal with Pearsons who admin this for DVSA and they make government depts look exceptionally efficient! They even make PFI contracts look good. Even Capita look good compared to these idiots! 
If I’d known this I would have done the 35 hours classroom version which requires no notification at DVLA or DVSA as it could actually be a lot quicker, albeit more sleepy. You just do it, then wait for the CPC card to arrive.