How do I remove a trojan?

Every time I start my browser, I get redirected to a random website and get a lot of pop-up ads. I think all this happens because I have a trojan on my computer, so I'd like to delete it. I tried installing an anti-malware application but it won't install. Please help.

There is an application called Malwarebytes Anti-Malware that deletes this kind of Trojans, do a search in google for it, download and install it.
If it doesn't work, I recommend you install Kaspersky Internet Security and try to clean every malicious application from your system.
Good Luck.