Upgraded to larger Instance, why can't I bring the old snapshots?

Could you clarify your question a bit?
Are you asking for a way to create a smaller instance from a snapshot of a larger instance?
I.e., you want to create a 512mb instance from a snapshot of a 1gb snapshot?

No, I have snapshots of my Lightsail instance that only existwith the smaller instance - my default creation.

I've upgraded to a larger Lightsail instance (you have to start a new one to do this), but if I delete my smaller instance I will lose my previous snapshots and therefore my default install pre-SSL and HSTS. So if something goes wrong with my security certificates in August, I can't just reload a pre-SSL version of my website to keep it going -> they will be deleted with my smaller instance!

Why can't I carry the snapshots over to the larger instance? It's just a backup/copy of an instance?

****If I go to my older smaller instance and go to my snapshots of this instance, the options for each snapshot are:
Create New Instance
Copy to Another Region
Copy to Amazon EC2
Delete Snapshot

No "Copy to another instance" which would be incredibly useful... as in I can't believe it's not there already...

Cheers for any help - might there be a way before I delete the smaller instance and lose that ability to restore from backup snapshots?

Are you talking about automatic snapshots?

If you keep an automatic snapshot, it gets listed (or copied to) in the main snapshot list and can be retained forever.

I created an instance last year, saved an automatic snapshot, and deleted the instance. I can still restore the snapshot to the same, or larger, instance anytime I want.

Thanks for your reply David.

This might answer my question then as I assumed if I delete the instance my Manually saved snapshots would also delete.

I don't use automatic snapshots, I take a snapshot at different stages of build so I can go back if needed (website isn't going to be dynamically changing, very static design).

I'm just worried if I delete an instance, the snapshots go with it. If they stick around, then you're right, I could re-install from my manual snapshots...?

See Below Screengrab - looks to me like if I hit delete on the smaller instance, I lose those 2 snapshots which are important...

https://imgur.com/a/lX9WWyP
https://imgur.com/a/DJJJcet

UPDATE: I just deleted the smaller instance, decided to just go for it based on your info.
IT DOES WORK! The snapshots are still there and I can create a new instance from them, THANK YOU SO MUCH DAVID!

David answered the question about deleting an instance - it doesn't delete your snapshots, they are separate entities so you can safely delete an instance, keep the snapshots of that instance and restore/create a new instance from those snapshots should you need to. Thanks David!