Q. What will happen if I use the complete allocated web space ?
Ans: Your web site can still work even though you reach the limit of your disk space quota.
Once you reach disk quota limits cPanel can send automated email notifications. If you ignore those notifications your web site can still work however incoming emails can get bounced and no new records are going to be further to your database.
For getting more disk space the only solution to this is to upgrade to next web hosting higher plan.
If you wish to upgrade your website hosting package feel free to contact our Billing Department through ticket or Live chat support.