IrfanView is a free, basic image viewer and editor for Windows. You can use it to convert multiple files in a folder from one format to another. You can download the program at https://www.irfanview.com/
- Open IrfanView.
- Open the File menu and choose Batch Conversion/Rename.

- Under the Work as section of the Batch Conversion window, select Batch Conversion.

- Using the Look in drop-down menu, find and open the folder which holds the images you wish to convert.

- Click the Create New Folder button to make a new folder to hold the converted files.

- In the Output folder pane, select the new folder using the Browse button.

- Click the Add all button to add all of the images from the input folder to the Input file list.

- In the Batch Conversion setting pane, choose an Output format.

- If you wish to resize the images in addition to changing the file format, check the Use advanced option (for bulk resizeā¦) checkbox and click the Advanced button.

- Under the RESIZE section of the options window enter new dimensions and click the OK button.

- Click the Start Batch button.

- When the batch conversion is complete, click the Exit Batch button.