Sorry for the delay in replying.
The Triban 500 uses a A-headset and as such has very little adjustment available to the height of the stem/bar. You can however, if this is not already the case, put the 5mm spacers under the stem and this will raise the stem.
Another way to gain height is to flip the stem upside down as this will change the angle of the stem.
You can use this steerer extender here.
Hope this helps.