Hi Akanksha,
On Portfolio view, click on the current date range on top right of the table, you can select the date range from the options in the list or specify the range be selecting the custom date range option, dates should be entered in the following format 'MM/DD/YYYY', also to compare the data with other date range , you can select a check box next to 'compare with' and click apply.
Hope this helps.
Regards
Nidhi