You didn't give any details about what makes up field b. B could be a calculation field or you could use set field.
Simply change the calculation field to type Number, Text, Date, TIme, TimeStamp--whichever matches the return type of the calculation and the current value produced by the calculation should be preserved as the data stored in what is now a data field instead of a calculation field. I've done this with a stored calculation. I haven't tried this with an unstored calculation field--which I suspect will not work, so check your storage option to make sure that this is a stored calculation.
You can also keep the calculation field and use Replace Field Contents to copy the contents of the calculation field into a data field defined to have the correct data type.
Field 'B' is a calculated result of Field 'A' i.e.
1.5 * A
but I want to eventually get rid of field 'A' and still retain the value originally obtained with the calculation.
Sorry for the confusion, I'm new to this...
Under Manage-Databases, select field b then under Auto-Enter select calculated value. Enter 1.5 * A. If you decide later to delete field A then goto field b and unselect the calculated value then delete field A.
Or tab into Field B and use Replace Field Contents, and set it to be by calculation, = Field A * 1.5.
Both fields will still be number, just as if you had copied and pasted values in Excel.