The first thing that I need to know is if you'd like to retain the data written on those tapes(considering that the there hasnt been a successfull backup since two weeks).
Based on the configuration you have, I assume you have configured Partitions. If possible, please set an a retention period (Overwrite Protection Period and Append Period) to the Media Set associated to the backup job. Ideally, based on the retention period, the tapes in the slots should be overwritten/appended.
Refer to An explanation of the "Overwrite Protection Period" and the "Append Period" : http://www.symantec.com/business/support/index?page=content&id=TECH5459
Since now the tapes are showing as 'Media Full', you could move them to scratch media and start the backup jobs.
Note: I'd suggest you to keep a copy of the last full backup job that ran successfully before associating the media to Scratch Media Set.
You could also add more slots(Slots 5, 4, 3..1) to this partition incase if they are not being used by any backup jobs.
You may refer to the following link to get more details on Configuring Partitions: http://www.symantec.com/business/support/index?page=content&id=TECH27909
As far as removing tapes from slots using Backup Exec is concerned, you need to ensure that your Robotic Library has a mail slot. If it does, then you need to select the slot and click on Export(located on the left, under Media Tasks section). You may refer to the following link to get more details on this: http://www.symantec.com/business/support/index?page=content&id=TECH34389