Nesting IF statements?

"Update" Worksheet is getting data from "Sum1" I'm trying to modify "Update" as follows

PART 1: If the cell is "0" remain "0"
PART 2: If the cell is a "positive number" remain a positive number.
PART 3: If the cell is a "negative Number" take the inverse of the
"negative number" and if that number is equal to it's "Column Row 1 Number"
OR greater than it's "Column Row 1 Number" Then that cell becomes "Column Row1 Number"
If the number is less than "Column Row1 Number" then remains that number.
Note: When PART 3 has been determined all PART 3 cells are returned to a Negative number.

Thanks for any help mark

Inverse number.... If Minus ( example -10) change to 10. Didn't know how to explain the math without doing this. Once Part3 calculation are done (they should all be positive) take that number and make it negative(example 6 would become -6)
Added Worksheet "what "update should Look Like" to help explain. Thanks for taking the time. Mark

Here is the updated spreadsheet.

Richard, It works perfectly, thank you for sharing your knowledge and time. I truly appreciate the help. Mark