Can the GT205-V (8 Channel Bio Amp from g.tec) be upgraded to a GT201-V (16 Channel Bio Amp)

This might depend on the serial number, but in general it is not feasible. The upgrade not only involves extra work, but also the certification process poses a problem. 
One could connect two GT205 to a 16 channel unit, but one has to be aware that the signal quality is decreased compared to one GT201, due to more lead wires to connect the grounds and the presence of two power supplies.