How do I increase an APSF partition?

I’m using the ‘intuitive’ High Sierra OSX for this. In the end I want to allocate around 400 GB’s of data to my main partition (BIGtb). I first tried converting all the partitions to ASPF in hopes that I could do a simple merge, which failed. I then converted the two partitions back to OSX Journaled.

I will post pics that I believe may be relative.

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