Hi Roland.
Fiat has different spec wheels for different countries, for India they still give us 4X98PCD, 15"diameter, ET 42, 6"wide wheels. Or 4X98pcd, 16" diameter, ET44, 6.5"wide.
where as in UK and other places, its 100pcd etc, etc.
check your user manual or service manual for your car model in your country and let us know the complete spec of the stock wheel and I/we will be able to guide you on correct spec wheel upgrade size options.
17" diameter wheels are okay(check pcd for fitment). you can go up to 7"wide wheels provided the offset is with in +/-2 of the factory and does not foul with the strut/wheel arches. 8"wide wheels might foul with wheel arch/strut etc.