Change dollar value(+credit) to (-)debits

ilmconsultant 

I am not sure what it means to turn a credit into a debit so maybe this is not the answer you require.  However, if you have unsigned lists of credits and debits they may be combined into a single transaction amount using the formula

transaction
= credit - debit

This does assume that the array of credits has the same number of rows.

ilmconsultant 

Using a formula:

=-C1

where the credit value is in C1.

Or change in place:

• Enter -1 in an empty cell.
• Copy this cell.
• Select the range with the positive values.
• Right-click in the selection.
• Select 'Paste Special...' from the context menu.
• Select Multiply.
• Click OK.
• You can now clear the cell in which you entered -1.