If the character has any unspent attribute points (AP), as shown at the bottom of the Attributes window, the [+] button to the left of each primary attribute will allow the player to spend these points. As long as the player hasn't confirmed his or her choice by pressing the "Accept" button (which will appear at the bottom, to the right of the "Attribute Points" number, if there are any unspent attribute points) he or she may also remove AP by pressing the [-] button to the left of the respective primary attribute. Once the player hits "Accept", the primary attributes and attribute points status is frozen.
The player may modify the character's armor by opening the backpack or footlocker simultanously with the attributes window. He/she may then equip pieces of armor by right-clicking them in the backpack/footlocker or by dragging them.