To edit access control on issue boards:
Go to issues in the main menu on the left.
In the top right of the new window you will find settings. Click the settings button.
From the new settings window you will find access control. Click access control button.
A list of the members with access will appear and the edit access button. Click the edit access button.
Define access for member(s) or team(s).
Administrators
Others: This is the access for all others then yourself, with an exception from admin user. The drop down menu has some options.
No access - Can't access the issue board.
Read - Have access to the issue board, but cannot create issues or make comments on existing issues.
Write and Read - Can create new issues and comment on existing issues.
Full access (all admin users) - Same as Write and Read but can also edit access on that specific issue board.
Owner: This is the access for the owner of the issue board. It has the same options as in point 7.