1- Install a security application
If you have not already done so, first thing you should do is install an application to protect your smartphone. Not only will help you to explore your device for malware but protect you from attacks from "phishing" (malicious web trying to deceive pages), and also tend to have other tools like filters against spam, functions burglar or even to establish parental controls, very useful, for example if it is a tablet using your children.
Typically this should be enough to clean your smartphone. Note that antivirus may give some kind of "false positive" indicating as malicious any app you have used for months without problem. In that case you can investigate other opinions of the app in question or simply ignore the warning if you think it is a safe program.
On the other hand, it is possible that some of the malware is able to confuse the antivirus security controls. If you think so you can take several alternatives such as the following.
2. Boot into safe mode and examines the apps manually
Boot into safe mode makes your phone starts only with the operating system without starting any third party app. To do this, usually you must press the power button and when leaving the shutdown or restart options press and hold the button to turn off until the reset option appears in safe mode. On some phones from brands like Samsung or Motorola method to boot into safe mode is different, so if it does not work above, must search Google "Start in Safe Mode xx" where xx is obviously the make and model of your phone.
3. Review the apps manually
Once you've booted into safe mode, go to settings and select the Applications option and make sure you're on the Downloaded tab. If you do not know the name of the application that can be still problematic, examine the list to view any application you are not sure you have installed or that you think should not be installed on your mobile. When you see any suspicious, click on it and the "UNINSTALL" button.
It is possible that some applications can not be desisntalar. The reason is that such application may be made administrator privileges on the device. To withdraw administrator permissions see the Security section and select Device Administrators. In this section, simply deselect the app that has taken administrator permissions and you can remove it.
4. Restart in normal mode
After removing the suspicious application, you can restart the phone to normal mode and install, if you have not done before, a security application and antivirus.
5. If all else fails, you can simply reset the phone
If you think that despite everything still some kind of malicious application on your phone, you can make a backup of important content such as photos and personal videos as well as your chats WhatsApp (you can copy into Google Drive), and proceed to reverse the phone to factory.
This process will erase the entire contents of your device, including malicious applications and must then reinstall your applications, email accounts, etc. (Which is not very complicated because Google retains associated with your account your message, logging and other apps installed).