Hi Yurple,
I'd advise you to upgrade to Anope 1.8.0 before carrying on as 1.7.21 is quite an old version now although still good it might be worth you looking at upgrading from a "Development" release to a "Stable" one.
Nonetheless; os_chgwhois.c which you linked to can be installed as follows:
Either Filezilla the os_chgwhois.c file to anope-1.7.21/src/modules (or it would be anope-1.8.0/src/modules)
Using PuTTY (yes you will need to or pm me and I'll have a look for you) cd to anope-1.7.21
make modules
make install
This will compile and install os_chgwhois.c to os_chgwhois.so and put it into the right place ~/services/modules normally.
You can then test this on IRC by using /msg operserv modload os_chgwhois and once you confirm it works OK, add it to services.conf to the ModulesAutoLoad section.
Any problems, either PM me on here, or drop into irc.anope.org #anope and someone'll help you