If this is a software where an end user opts to install the software, you can go to start>control panel>programs and features then uninstall the search engine software by selecting the install. Make sure you are not deleting the wrong thing (you can google each installed program to try and verify it).
tiip:
Sorting the installed programs by the last date of install will help find the culprit if it is a recent addition.
Also if using internet explorer, go to tools>options (press alt to make the menu appear). You can change the setting to use blank. Then change it to whatever you need. Sometimes the registry setting is altered so that the use default also refers to the website you do not want so blank is a good alternative. If the offending search engine is overriding these settings, it may also be an add-on.
I'll cover internet explorer and firefox, google chrome browser does not have this issue (yet)
To access the default settings of internet explorer launch internet explorer and go to tools>internet options:
There are three options on the general tab: use current, use derfault, use blank. Try default or blank to override settings.
If the add-on won't allow this try removing the addon or installed software.
You can manage add-ons for internet explorer via tools>internet options>programs>manage add-ons: (simply turn the add-on off or remove it).
similar in firefox (tools>options>general tab) - (press alt if the tools option does not appear at the top)
home page 'use current' or restore to default'.
If this does not work, remove the installed software or delete/turn off the add-on
to manage/remove add-ons go to tools>ad-ons
