I converted my spreadsheet into a web application. I need to make some changes in my workbook. Do I have to go through the whole conversion process again?

Depends on the changes. If the changes are related to the user interface portion of your workbook, then the answer is Yes. You have to run the SpreadsheetWEB’s conversion wizard again but it uses stored parameters like selected input cells etc from the previous conversion, which makes all subsequent conversions much faster.

If the changes are outside the user interface and related to formulas or data, then the answer is No. Simply save the workbook you had previously converted and upload it to SpreadsheetWEB server. Your changes will be live immediately.