156 Oil type

I know a lot of questions have been posted and answered about Alfa oil types
& recommendations but I have another one! Its coming up to oil change time
but this is the first time I have changed the oil since i bought the car.
Ive had it just under a year and done about 6-7000 miles. It is a 2000 156
2.0 Selespeed. I bought it privately and even now the oil is still very
clean and the level has dropped little but i dont know what type of oil is
in it - standard, semi or fully synthetic. I know fully synthetic is
recommended and that is what i want to use but i have heard that if you
change from non synthetic to synthetic then deposit can dislodge from the
engine because of the new type of oil. Is this true and Is there any way to
find out what oil is in it?

Any help would be appreciated

Stuart