The leaves are starting to turn lighter in color not quite yellow yet.
If the yellowing is confined to the fresh leaves then it is nothing to worry about, it is a characteristic of Ficus at least mine are like this. If the overall plant is yellowing then that is a sign of a problem. Perhaps over-watering, (watering too frequently) low light levels or both. It would really help if you are able to provide some supplemental lighting.
It had glued stone on top, which i removed after reading here. The soil is 99percent pottting soil with some styrofoam in it.
Good move in removing the rocks. The Styrofoam is probably Perlite, a common ingredient in potting soil.
Should i get different soil and transplant now or wait.
Ficus are pretty tolerant of this type of soil. I would rather see it in a more free draining medium but if you manage your watering properly it should be OK. For now it might be best to concentrate on providing it a better environment, lighting and warmth will go a long way. Besides there is no point in re-potting it into a similar medium so you will have to acquire a better medium first anyway.