Licence issue

Good afternoon ,
When I attempt to modify a codeunit .
I m getting the message error :
You do not have the permission to insert into the G/L entry table

When I attempt to create a code unit .
I m getting the message error :
You do not have the permission to create a codeunit contact your system administrator to have your permission changed .

I wonder how can a make sure I have the right licence .
Where I need to go to verify the type of licence I m using ?
And what I need to do to get a developer licence ?

I m using NAV 2016

For end-users there is no such thing as a “developer license”. Only "developer’ granules. Which you add to your license to achieve the desired functionality. To modify protected tables (i.e. G/L Entry) you would need to add the “Solution Developer” granule. Along with its prerequisites.