You are not clear on what you want to do but from what I understand, you want to change the x labels from 0-2-4-6.. to something else. Below is such an example;
x = 1:1e-2:2*pi; % sample x data
y = sin(x); % sample y data
plot(x,y)
set(gca,'XTick',[1:1:7]) % shows 1 2 3 .. 7 in x axis
str1 = {'a','b','c','x','y','z','q'}; % cell array to replace 1 2 3 .. 7
set(gca,'XTickLabel',str1) % replace x axis values
