First one is re-sizing the image using the Image Size dialog box. To open the Image Size dialog box follow the menu Image > Image Size or use the shortcut of Ctrl+Alt+I.
In this dialog box you may see the image dimensions in pixels and other unit of general measurements (like inches, cm, mm, etc.). You can adjust the width or height using the Document Size section by changing the values.
While changing the values concern on the width and height ratio. If you need to keep the ratio unchanged use the Constrain Properties check box checked. While checked this you only can change one of the width or height and the other one is automatically adjusted constraining the ratio.
The second method is using the crop tool. To activate the crop tool use the shortcut C.
In the Options toolbar give the width and height with the unit and resolution to crop and drag on the image to resize the image area you want. (If you do not see the Options toolbar click on Window > Options) While giving the unit do it as follows. (I.e. 860 px) Use px for pixels, cm for centimeters, mm for milimeters, inch for inches, etc. Press <ENTER> to complete the crop.