Check "Replace"

Delete the "Replace this" field. By deleting it you will replace the whole name.

Define the "Replace by this" field as "$" or "$$" or "$$$" and so on. Depending on how many leading zeroes you want. So a "$" would make the numbering start as "1" and "$$" would make it start as "01".

You may also define the start value. If you want the numbering start from 20 on then change to expert mode (by pressing F2) and set it there:

Click here to find out how to number downwards from 100 to 1 instead of 1 to 100.