The best way to deal with this, is to configure and use WmMonitor Archive components.
After that you have 3 choices for deleting data:
1- Use stored procedures (if you know the syntax).
2- Use Monitor built in services.
3- Use MWS UI porlets.
As far as I remember WM* tables are used only for auditing and not runtime. If you delete data you loose audit information, that’s all.
Anyway configure and use Archive from WmMonitor.
#webMethods-Archive#If-it-doesn-t-fit-anywhere-else#webMethods