You can edit a deck's post type, post spacing and post depth. You can also disable posts altogether if you want.
To edit deck post properties:
Select the deck by clicking on one of its edges.
Right-click and select Properties, or select Edit > Modify Elements > Properties.
In the Decks dialog, select the Support tab.
If you want to remove posts from the deck, uncheck the Include Posts check box in the Supports area.
To select a different member to use for deck posts, click the Select button next to the Include Posts edit box, then make your selection from the catalog.
To edit the properties of the currently selected member, click the Edit button, then make the desired changes in the Columns dialog.
To change the spacing between posts along beams, edit the value in the Spacing along Beam edit box.
To change the depth of the posts in the ground, edit the value in the Depth below ground level edit box. This effectively changes the overall height of the post, but does not affect the portion shown above ground.
Click OK.