The apostrophe isn't really part of the cell content, it just signifies that the cell is formatted as text. To reenter all the data as number:
- Highlight all of the cells and use Format -> Cells to change the cell format to an appropriate number format.
- With all of the cells still selected, go to the menu Edit -> Find & Replace
- In the Search For box enter .* (period asterisk)
- In the Replace with box enter &
- Select More Options and check Current Selection Only and Regular Expressions
- Click Replace All
The .* "means zero or more of any character" and & means "whatever was found". These are regular expressions which are explained in the help section