For your first question, Go to Cloudera Manager -> HDFS -> Configuration -> search for 'Log Directory' -> change the dir path wherever applicable
For your second question, Go to Cloudera Manager -> HDFS -> Configuration -> search for 'maximum log' -> Here you can change both Max log file size & Number of log files to retain.
Maximum Audit Log File Size - 100 Mib (You can reduce the size)
Number of Audit Logs to Retain - 10 (you can reduce how many logs to retain)
Finally, you can do this for all the applicable services like yarn, etc