Run the Release engineering item revision process to release the engineering item revision of the item selected on the Engineering structure form. The status is changed from 'Not released' to 'Released'. The status of any previous revisions is changed to 'Released, but not the last released revision'.
An engineering item revision can be released only if all items of the engineering BOM have been released. To release all revisions from the BOM during the execution of the process, select the Also release all underlying revisions check box.
Select the Only allow last released revisions of underlying lines check box to have the software check whether the engineering BOM contains released engineering item revisions that are not the last released revisions. If the check box is selected and the engineering BOM contains revisions for which a more recent released revision exists, releases will not be processed properly. Click the Check button to check which BOM line contains a revision that is not the last released revision. BOM lines with the following icons require your attention:
The revision is not the last released revision; a more recent released revision exists. For a BOM line like this, you need to make sure that the BOM contains only the last released revisions before you can resume the release. If you leave the Only allow last released revisions of underlying lines check box empty, you can choose whether to use this revision or not.
The revision is not the last revision, but it is the revision that was released most recently. The more recent revision has not been released yet. If you want to use the most recent revision, you need to release it first.
Use the settings in the Synchronization section to specify that the engineering item revision is to be synchronized automatically with the part or production file once the revision has been released.
Also release all underlying revisions
The revision is not the last released revision; a more recent released revision exists. For a BOM line like this, you need to make sure that the BOM contains only the last released revisions before you can resume the release. If you leave the 
The revision is not the last revision, but it is the revision that was released most recently. The more recent revision has not been released yet. If you want to use the most recent revision, you need to release it first.