You can edit your issues in MS Excel sheet and then apply the changes in Jira. Every cell that you edit will change color to orange color and whole row will become yellow. This way you can easily track changes you made in excel sheet.
In order to apply these changes just click Send Issue to Jira button (1). You will be asked to confirm and if everything was filled in correctly, after pressing "Yes" button on "Confirmation" prompt (2), the rows will turn back white.