Step 1: Click 
next to the name of the space. Select permissions.
Step 2: . Scroll down to Individual users sections
Step 3: Type a user's name and select from the drop down list. Then click on add
Step 4: Edit permissions by checking or unchecking the checkboxes.To delete a user, simply uncheck the boxes that appear next to their username and click on save.
Step 5: Click on Save all