Follow the below steps
- go to window menu in photoshop and select Action (or click alt+f9)
- create new action by clicking below icon in photoshop
- give any name to your action press record
- go to image size in image menu give any size you want
- save and close image after that stop your action
- now your action ready to perform multiple job
- go to the file menu and select the automate and go to batch
- select any folder in source and press ok