Hi,
to do this you can use condition, I have set these condition on your site:
- if "Grade" field equal to custom value "" hide "from" and "to" fields
- if "qualification_obtained" field equal to custom value "" hide "from_2" and "to_2" fields
We have attached a screenshot to explain you how make conditions. This screenshot become from parameter of "grade" field
we have found some problem on your template css for select and we have added these two lines on your custom.css
.chzn-container-single .chzn-drop, .chzn-container .chzn-drop{box-sizing:border-box !important;}
.chzn-container-single .chzn-search{display:none;}