To open the Tempo Property dialog box, you can either select the Object Select icon from the Layout Tab, or if you have a dynamic or tempo marking selected you can hover over the tempo marking and single click it.
There are 2 properties to a tempo marking.
Beats per Minute (bpm)
You can change the tempo marking Beats per Minute (bpm).
A tempo marking can be hidden. This is useful if you wish to create a series of tempo changes in each measure to simulate a realistic playback. The shortcut to hide a symbol is to hover over the tempo marking, and press H.