to install this module simply follow the canonical procedure
for installing any perl module

  $ tar zxvf Apache-SizeLimit-0.XX.tar.gz
  $ cd Apache-SizeLimit-0.XX

  $ perl Makefile.PL
    For static  mod_perl use -httpd /path/to/httpd
    For dynamic mod_perl use -apxs /path/to/apxs
  $ make
  $ sudo make install

for further directions, see the README.