I am not being able to change the emission factor that is highlighted in the attached picture.

The LEAP manual is not helping much :(

Can anyone advise how to change it? I want to use the 2006 IPCC guidelines

The table at the bottom of the screen is not editable - it (and the chart view) summarize the results calculated from the expressions shown in the table above it. However, you probably will need to edit the expression within "Current Accounts". In the screen you shared you are looking at a scenario.