You draw it's power triangle, then combine the power triangle at the new desired power factor so that from that power triangle you may found the kvar. the Difference between two triangles is the your required kvar for desired power factor.
At 0.85 power factor kvar=619.74
At 0.98 power factor kvar=203.05
so you required 416.68 kvar to improve your power factor to 0.98 from 0.85