How to restore backup file

My problem started when i upload my new theme.

I have the new theme activated on my wp but it keeps on showing the previous one, so i’ve decided to delete some old files using my FTP acct. But now it doesn’t give me any option to login to my wp admin. It’s just a blank page. And I tried to check my website glow.com.sa, which is now become blank page too.

I’m trying to restore my backup files in PHPMyAdmin and it gives me an error message that the file being upload is too large. The backup file is 481MB.

Please help me with this. I’m just new in WP.