Mustafa - in the callback for the first slider you could try something like
function slider1_Callback(hObject, eventdata, handles)
taper = get(hObject,'value') ;
set(handles.texttaper,'string',num2str(taper));
set(handles.sliderrs, 'Max', taper);
But you would need to add some logic to make sure that the max value you are using (taper) is valid given the minimum value for that other slider else you may see warning messages like
Warning: slider control requires that Min be less than Max
Control will not be rendered until all of its parameter values are valid
