first take a back up of site then check each file or use any free site scanner like https://sitecheck.sucuri.net/
in report you will see which files are affected by malware or best use google web master tool this helps lot, webmaster tool can show you infected files with code then after just simply delete infected code or replace file if you have old data which is clean.
Once you done with cleaning, request google web master tool to verify site, this is for as in chorme or other browsers you can see its warning about your site that site having malware right? this will remove from your site.
if you need any help let me know