Log into your IWeb account
Select "Account Management" then "Stock Movements"
Set the dates and click 'Search' (if you've made many trades it may take a few minutes for them all to be displayed).
Select all the information in the table, excluding the headings and totals, and copy to the clipboard (now may be a good time to save the data by pasting into Notepad).
Paste the IWeb trade information into the text box on the convert format page.
Select the appropriate option and click the "CONVERT" button to convert the trade information (note you can paste the resulting file directly into a spreadsheet and save if you wish)
Example IWeb file
File in correct format
General Info
Each trade in the trade history typically ends with the text "Trade in the Market". However there are exceptions such as share restructurings and situations when cash is paid to you upon liquidation or cash back. I had to manually remove a few trades such as these because they had been shown twice or were just plain erroneous. So it may be worth while just spending a few minutes browsing through your trades to make sure everything looks OK.