Conversion from .22 to .25 WH100

I am assuming since the Weihrauch WH100 is manufactured in .25 that i should be able to change mine to .25.

What would be involved? Not possible to do so in .30?

Context, I live on acreage in San Diego County and have lots of game from turkeys, coyotes, and bob cat, with pigs not far away amd expanding. I am pondering a conversion of my WH100 full length thumbhole, to .25 for shooting slugs with pin point accuracy at the above critters out to 60 yards.

Wondering what would be involved. Would love some pointers in the right direction for research.

Thank you,
Jon