Sam - you will need to maipulate then ticks and tick labels for the x-axis. Try running the following statements
xticks = get(gca,'XTick');
xtickLabels = get(gca,'XTickLabel');
Both of these statements should return vectors/arrays of the positions and labels of the x-axis ticks respectively. Since you want to remove every other label (due to the 0.5), then just reset these two properties if the x-axis using every other element only as
set(gca,'XTick',xticks(1:2:end), 'XTickLabel',xtickLabels(1:2:end));
Note that 1:2:end means start at the first element (at index 1) and jump by two until the end is reached. gca is the handle to the current axis (g is for get). The above may require some changes given your version of MATLAB, but try it out anyway.
EDIT
If xtickLabels is a character array, then the above set should be replaced with
set(gca,'XTick',xticks(1:2:end), 'XTickLabel',xtickLabels(1:2:end,:));
