To convert to an EASA ATPL you must have:
ICAO ATPL (NOT Frozen) with current Type Rating.
EASA Class 1 Medical (Issued by country you want to issue your licence).
Passes in ALL 14 ATPL theory exams (Yes, you are exempt approved training course if you hold an ICAO ATPL).
1,500 hrs Total Time, of which:
500 Hours Multi Crew
500 Hours PICUS (or 250 Hours PIC / 250 Hours PICUS)
200 Hours Cross Country (100 Hours PIC/PICUS)
75 Hours Instrument Flight Time (NOT only IFR - 4 Hours IFR = 1 Hour Instrument Flight no longer applies)
100 Hours Night
You must then pass an ATPL Skills Test on the aircraft/sim currently held in your ICAO ATPL. If you want a different Type Rating you must also provide evidence of having succesfully completed a TR Course on that aircraft type at an approved TRTO.
I think that covers it - apologies if I've missed anything but it's home time and I have a long drive ahead of me!!!