How can I remove un-used CSS, Images & JS codes from my project?
If a project is bigger; usually there are lots of trash codes specifically if the project is built based on another similar project.
May be its late for this answer but, i have the same thinking an i can just tell you to few options. There is NodeJS powered libraries doing the cleaning unused css selectors. Some of them really smart even if you used merged class name parts in javascript. You can find those just by google it like "remove unused css"
And, i find the few videos on youtube about same topic. One of them using Visual Studio for this job but i dont tried this. Link here: Youtube Link
Another option is Chrome Dev Tool. Just use chrome developer tools audits tab.
Sorry for little confusing text but i have only those. I hope it will fix your problem or satisfy expectations.