Listen. Amp capacitors can hold a lethal charge for days after you unplug the thing. They are the silent ninjas of the electronics world. If you’re not comfortable with this, hire a pro. Your fingers are worth more than any vintage Fender.
That said, if you’re still here, congratulations on your gambling addiction. Before you touch anything internal, unplug the amp, then hold the power switch down for thirty seconds. This helps drain the caps, but never trust them fully. Use a multimeter to check for zero voltage.