You may need to change the value in a cell when working with the attribute table. Depending on your workflow, your edits may all be grouped together, or you may need to browse your table for scattered updates. Follow the steps below to learn the options to edit individual cell values in an attribute table.
Note:
Some tables are not editable, such as text files (.xls, .xlsx, .txt, and .csv, for example). These tables are read-only. If you edit this data externally, you must add the text file to the project again. However, Microsoft Excel workbook files can be refreshed.
Once a table view is open, the highlighted cell is ready for editing. When you first open a table, the first cell of the first column and row is highlighted by default. Some attributes are not editable, such as managed fields like ObjectID, Shape_Length, and Shape_Area. Typically, the ObjectID field is the first in the table list. You must browse the table to find the cell you want to edit. You can edit any nonrestricted field once it is highlighted.
To edit a cell value, type a value directly in the highlighted cell. You do not need to activate the cell to begin editing. The field name and row header turn green with a pencil icon 
when editing.
You can also edit a cell value by doing one of the following:
- Right-click for clipboard options.
- Double-click to access the calendar to choose a date or time.
- Double-click to access a drop-down menu if the field contains domains.
- Press F2 to activate the cell you want to edit.
- Press Ctrl+F to display the Find and Replace controls to make specific updates to individual values in an iterative process or update multiple values at once.
Press Enter to apply your edits to the table. The active cell moves down to the next row in the table and you can continue to make changes. Closing the table applies any pending edits. You can undo and redo these edits to the table, as the changes are not yet committed to the database. When you are finished and ready to commit your edits to the database, click Save Edits 
in the Manage Edits group, which for tables opened from a map is found on the Edit tab and is found on the Table tab for tables opened from the Catalog view or Catalog pane.