Under the Manintenance options submenu, the plugin can be reset to the default options via clicking the Reset all options to defaults button.
The reset means:
All plugin options will reset to defaults (caching, compatibility, index table and statistics options)
The search instance options will not be changed
The database tables, contents and the files will not be deleted either.
By disabling and removing the plugin via the plugin manager, all the plugin options, including the search instances, will remain in the database.
Under the Manintenance options submenu, the plugin can be reset to the default options via clicking the Wipe all plugin data & deactivate Ajax Search Pro button.
The wipe means:
All plugin options will be deleted
The search instances will be deleted
The database tables and the files will be deleted
The plugin will deactivate and redirect to the plugin manager screen after, where you can delete it or re-install it again.
After wiping all data, the plugin can be deleted via the plugin manager.