@oristarA,
Self concept is broader than self esteem, I think. It is about our entire picture of ourselves whereas self-esteem is about whether we think well of ourselves or not.
Therefore self concept will have major importance in self esteem and vice versa but I do not think they are completely interchangeable.
For instance, whether we are male or female will affect our self concept, but may or may not affect our self-esteem. If we are in a highly patriarchal culture it may lower our self esteem, in other cultures it may be neutral or increase self esteem.
It is part of my self concept that I have brown hair and blue eyes.....but that is pretty neutral in my self esteem as I neither especially like nor dislike brown hair and blue eyes.
If I desperately wanted to have blonde hair or brown eyes, then these factors might affect my self esteem.