The amount of hours you will need to redo will depend on a number of factors, including how far you got in the 25 you have already done and how quickly you can pick everything up again.
If you can, I would probably suggest budgeting for 30 hours of training and doing them intensively. Anything left over you could use to treat yourself to some post test flying, a tailwheel conversion or learning on a new aircraft for example.
You didn't make clear whether you have sat the ground exams or just took the classes. There is no requirement to take any classes for the PPL ground exams, you may just learn yourself and take the ground exams when you are ready. I will presume that you have taken ground exams as you have solo time so you must have taken Air Law at least. I am not sure whether these are still usable after a year, someone will be along shortly who does know though!
Good luck and welcome to PPRuNe!