The attitude is there because a simple search would have told you the answer, plus it is in the OP. Repeating the same answer to the same question does get a tad annoying. I could quite easily have just told you where to look, or even just ignored the question.
No, calibre is not an image editor. If you open it in MSPaint you should then be able to save as a .PNG file. N.B. it also has to have the correct name, also in the OP, which is dependant on the kindle in question.
Else you could add the copy cover to kindle plugin to Calibre made by Jackie_w to do the whole process for you on multiple covers at once.