Open Syslog Viewer on your server. Goto Settings under File and you can adjust the slider to suit your needs.
Interface details and retention can be edited here;
Here are the top 2 tables that consume most of the DB, considering you have no other modules
If you did not used it you can truncate it.
open database manager
run this commands
1. truncate table TRAPS
2. truncate table TRAPVARBINDS
And if you received traps that you think is not that critical or important to your environment, you can use "discard messages" option
Start -> Program Files -> Solarwinds -> Orion -> Syslog Viewer
From this tool, Goto File -> Trap Server settings -> Alert/Filter Rules Tab
II. To check retention of syslog: Open Syslog Viewer>File>Setting> check the Bar where "REtain syslog Messages in the database for 7 days"
III. To check retention of Traps: Open Trap Viewer>File>Setting> check the Bar where "Retain Trap Messages in the database for 7 days"
IV. To check retention of interface traffic: Open System Manager>File>Orion Network Performance Monitor Settings
(IN V9.5 higher) Open Web console> Admin> NPM Settings