what happens when you heat a transistor what normally would happen to the currents

 

It gets warmer.

Without more information, that's about all that can be said since it depends on the circuit it is in.

 

Is this a bipolar transistor or a field-effect transistor?

 

In a transistor (in any material) electrons are attached to their parent atoms and are to be dislodged by applying Energy(Voltage) to make them flow - which is called current fllow.
The amount of energy required, to dislodge depending upon how strongly they are attached/bonded to their parent. Heat ,light are also different forms of energies which when applied will dislodge electrons and there by increase the current flow.

 

But just heating a transistor does not mean that more current will flow. If the transistor is in a circuit driven by a current source, then the current won't change but the voltage across it will. Also, there are other factors at play in different types of transistors. CMOS circuits, for instance, because faster at very low temperatures and at very high temperatures due to different phenomena.