To me, there is no specific difference. Accent, Dialect, and Language are just nominal points on a continuum of difference.
As the others have said, typically an accent has slightly different pronunciations for some sounds, and a few different words. A dialect has a greater difference in sound, and a lot more different words.
A dialect can be considered a different language when it has substantially different sounds, and many different words.
And at the other end of the spectrum, there are languages that are completely different, like Chinese and English, where the only similarities are loanwords.
But when are two different ways of talking different accents, different dialects, or different languages? That's when it gets complicated, particularly when, as A☤P (Manu) mentioned, politics gets involved. There are no fixed rules.
In the west, we consider Cantonese to be a different language to Mandarin. But in China, they consider it a different dialect. I guess that's because they like to promote the idea of unity.
On the other hand, Portuguese, Spanish, and Italian are widely accepted as being different languages, yet in some ways, the differences between them are less than the differences between some dialects. The same is possibly true with some of the Scandinavian languages.
Are American English, and British English different accents? Or different dialects? I think they are accents, but some people might say they are dialects.