These alerts are on sepm or on client you want to clear out.
in sepm log retention period is 30 days by default, those will be cleared out.
client logs are stored under logs folder c:\program data\symantec
or
C:\Documents and Settings\All Users\Application Data\Symantec\Symantec AntiVirus Corporate Edition\7.5
add whatever you want to the below batch file
del c:\Windows\temp\SEP_INST.LOG.back
del c:\Program Files\Symantec\Symantec Endpoint Protection Manager\db\sem5.log.back
del c:\Program Files\Symantec\Symantec Endpoint Protection Manager\tomcat\logs\SesmLu.log.back
del c:\Program Files\Symantec\Symantec Endpoint Protection Manager\tomcat\logs\SesmLu-1.log.back
del c:\Program Files\Symantec\Symantec Endpoint Protection Manager\tomcat\logs\SesmLu-2.log.back
ren c:\Windows\temp\SEP_INST.LOG c:\Windows\temp\SEP_INST.LOG.Back
ren c:\Program Files\Symantec\Symantec Endpoint Protection Manager\db\sem5.log c:\Program Files\Symantec\Symantec Endpoint Protection Manager\db\sem5.log.back
ren c:\Program Files\Symantec\Symantec Endpoint Protection Manager\tomcat\logs\SesmLu.log c:\Program Files\Symantec\Symantec Endpoint Protection Manager\tomcat\logs\SesmLu.log.back
ren c:\Program Files\Symantec\Symantec Endpoint Protection Manager\tomcat\logs\SesmLu-1.log c:\Program Files\Symantec\Symantec Endpoint Protection Manager\tomcat\logs\SesmLu-1.log.back
ren c:\Program Files\Symantec\Symantec Endpoint Protection Manager\tomcat\logs\SesmLu-2.log c:\Program Files\Symantec\Symantec Endpoint Protection Manager\tomcat\logs\SesmLu-2.log.back