I'm thinking about changing the soil, can anyone help me, it grows indoors under light and also at the window when the sun is out. I'm ok to change the soil now? Should I leave the old soil close to the roots and just work around it? Which soil should I get? Thanks in advance

How long have you had the tree?

A year

That is great, well done. Most tropicals can be repotted in summer, but early spring is proboably better. Grown indoors under artificial light may limit the benefit of spring repotting.

The best soil is the one that holds water but goes from wet to slightly moist in 2-3 days under your conditions. Most bonsai enthusiasts reduce organic content more and more as they develop in the hobby. I think around 20% bark is a good option. Rest is unorganic. Pumice, lava rock, cat litter, absorber clay etc. It takes some time to find the perfect mix for ones own conditions.