Steps are as follows :
1) log in to your linux server as root user through SSH.
2) Go to the respective log directory via cd command for e.g cd/var/log/apache2 & enter following command one by one.
3) mv access_log access_log.old
4) mv error_log error_log.old
5) apachectl graceful
6) sleep 600
The first two commands will move the files, then command apachectl graceful will restart the apache server and last command will wait for 600 second for logging old request. The new requests will be logged on new files.