I had to replace a few lamps on the instrumentation panel on my '94 Corsa - don't know what year yours is -so here's how I done mine -
Unscrew the shroud surrounding the steering column and unscrew the surround of the instrumentation panel - you will have to disconnect the speedometer cable down at the gearbox end of it - simply unscrews - that will give enough slack to pull the instrument panel forwards towards you giving access to rear of panel to change blown lamps.
If it's the panel lights on the heater switches thats a different matter - I found it best to follow the instructions in a Haynes manual- unfortunately I dont have that now.