Pretty easy.
The Series 80 has a firing pin lock plunger & spring in the slide.
So take the slide off, just as if field stripping for cleaning.
Then use a small punch, or ball point pen, or something to push the FP in past the retainer plate and slide it off.
Then depress the FP lock in the bottom of the slide to release the firing pin & spring and catch it when it comes flying out.
Reassemble in reverse order.
But I really seriously doubt your FP spring needs to be replaced anyway, unless the gun has a lot of rounds through it, or has been dry-fired about a gazillion times.
And it doesn't need the extra power Wolff FP spring to prevent drop firing anyway, because it's already got a FP drop-safety lock.
rc