How to remove malware from wordpress site?

Hi , I have hosted my website in hostgator and i received mail from sitelock saying my website has malware. So, i tried to login to wp-admin dashboard . I am able to log in but i cannot get access to any page it says “error 403 forbidden ” so i spoke to peoples from hostgator . As per them i will have to download my website in local computer and scan with antivirus and remove any malicious code. So i download my site from cpanel. At this stage i am very unsure of which antivirus software i have to use and which code code malicious or what malicious code looks like. But i still scanned my site file with avast antivirus. it did said 1969 threats found and removed . After that i upload my site back from cpanel and creted new database and everything but its not working anymore . its saying “HTTP 500 internal server error”. i do have backup file which is already infected with malware. Is there any way i can remove malware from the site. and i am not in the stage of creating new site again from scratch.