As you have not mentioned what browser you are using I will explain how to change the search engines to the most used browser applications.
In Google Chrome simply right click inside the URL bar and select Edit Search Engines and from the windows that appear delete the unnecessary search engines.
In Mozilla Firefox, click the icon in the search field next to the URL bar and select Manage Search Engines.
In Internet Explorer explorer click the arrow found under the browser close button, as shown in the picture below and then Manage Search Providers.
Please note that if the search engine was installed due to an extension install then visit add-ons menus (Tools > Addons in Firefox, Tools > Extensions in Chrome and Tools > Manage Add-ons in Internet Explorer) in order to remove the installed extension.