How to get all sets to expire/delete before a Full backup runs?

[BackupBritney]

My Storage is not much bigger than what I want to backup, so I need all sets to expire before a Full backup runs.

I can make a Full backup every 4 weeks, keep for 27 days, this works at having one set on my Storage at any given time.

But this doesn't let me do Incremental, that I'd like daily, keep for 1 week.

The problem is that on the day 26, the Incremental runs, and on the day 27, no sets are deleted when that next Full comes about on day 28.

Am I limited to Incrementals that expire in 1 day ?

[Gurvinder]

set 2 day retention on Incrementals and maybe 3 weeks for Full. Also ensure this setting is enabled
Allow Backup Exec to delete all expired backup sets
click the Backup Exec button > Configuration and Settings > Backup Exec Settings > Storage

Note: Would recommend to have atleast space for 2 sets. That way you  have a backup set available all the time. 

[RogRubin]

More a general comment as I am concerned about this part of your strategy " so I need all sets to expire before a Full backup runs."
If I understand this correctly; then before you run your full backup, you expire all your backup sets, meaning at that particular time you have no data to restore from in case of a disaster or if your full backup would fail for whatever reason till you managed to run a new complete full backup successfully.
If the above is correct; then I would recommend you look at your strategy and maybe consider adding more space to your current target location or adding a secondary target location where you could duplicate your backup sets too (even if it is just the Full backup once); that way you have at least the possibility to restore from that duplicate backup set in a worst case scenario.