Copy Folders to FTP

I downloaded a theme from Theme Forest yesterday, but when I tried to upload using wordpress it freezes every time. I have seen some posts that say to try uploading to FTP. I am not sure how to do this. I thought I could copy and paste from my computer to my FTP folder, and I’ve also tried click and drag but it doesnt work.

How to I move a folder from my computer to my FTP? I am very new at this so if it could be explained in simple terms that would be great.

Are you using an FTP client?