By default SharePoint stores it’s usage logs in
C:Program Files Common Files Microsoft Shared Web Server Extensions14LOGS
but if a server doesn’t have a large C: drive then it is easy to change the location to a larger drive. Here is how:
1. Log in to Central Administration
2. In the Monitoring section click on Configure usage and health data collection
3. Change the path for the logs and the maximum size and then click OK
The change takes immediate effect, no services need to be restarted.
Note: the specified location must exist on all servers in the farm