how to convert .png to .jpg

simple command via terminal with mogrify command.

Open the terminal : Applications - Accessories - Terminal.
go to folder which your file to convert.
here for example :

$ cd /home/retnet/Desktop/picture/

and type in your terminal :

$ mogrify -format jpg *.png

now you can delete .png format via terminal :

$ rm *.png
or
$ rm /destination/folder/to-delete/*.png