use ACDsee 5.0Renaming a group of files or folders You can use the Batch Rename tool to rename a group of files or folders using a naming template. To rename a group of files or folders: In the Browser, select more than one file or folder. Click Edit | Batch Rename. In the Batch Rename dialog box, select or change the options. Click OK. Batch rename options Template Select the Use template for renaming files check box if you would like to rename the files using a template. Select one of the following two options to use either numeric or alphabetic characters in the template: Use numbers to replace #'s: This option replaces any number signs (#) in the template name with numeric characters. Click the Start at spin box arrows or type a value to specify the starting number of the sequence. Use letters to replace #'s: This option replaces any number signs (#) in the template name with alphabetic characters. Click the Start at spin box arrows or type a value to specify the starting letter of the sequence

come ini am not sure whether the method mentioned by Cowboy will do, by only renaming the files. if not, try this, also using ACDsee: select multiple picture files, choose from menu bar: activity -> edit -> convert; then convert the pictures in bmp format into jpg format. you could also search on google for tools.

发现还是没有任何区别大小依旧没有变化，难道只能用save as 才可以？！ 郁闷！