This is a beginner question, so while I'll give you some pointers, you may want to consider contracting a sysadmin to help you out, or asking your host.
Apache logs are often stored in different places depending on the configuration of the server. To find them, you'll want to check your Apache configuration file. Do a `locate httpd.conf` to find out where it is, probably in /usr/local/apache/conf.
Once you've found the Apache config file, do `grep Log <httpd.conf location>` and you will get a number of resulting lines. The file you are most interested in will begin with CustomLog or TransferLog, however there are usually other log files such as ErrorLog, RefererLog, and so on that you may also wish to rotate.
The logrotate(8) program is reasonably good at rotating log files for you. The man page `man logrotate` can help you learn how to configure it, if installed.