Yes, you need to change the soil. But bagged or pre-made 'bonsai soil' is not what you want.
See the link below. Lucy's first post will give you all the info you need for success. Plus, mixing
your own potting medium, in small quantities, is really not too expensive.
Certainly not as expensive as replacing plants ;)

Josh

Here is a link that might be useful: Repotting a Ficus

I have one from Home Depot a decade and a half old. What i would concentrate on if i had a second chance is getting the roots looking good and growing evenly in all directions. Try not to underpot it. They can be very well started off considering they are for mass production plants..just need more help.
I should post a pic of my old Home Depot Ficus nitida. Not my best, but a very hardy plant.
A local Bonsai nursery had a Ficus nitida with perfect roots-even in all directions.Just perfect.Every inch,circling the trunk a root the same thickness as it's neighbor. They do though put up a fight to layer the canopy. Even that $1,000 Bonsai was of a simple solid canopy,topiaried in a pyramidal shape.

can u post a pic after u get it