That is a large blister.
It will need to be drained. It will burst anyway if left as it is but that would not be sterile.
if you can consult a doctor immediately, he/she can clean the blister and then rain it surgically. if that is possible, please do it at home.
Buy sterile cotton swabs and a bottle of clinical spirit or rubbing alcohol. Also buy a sterile needle - the type used for injections will do. These are available at any medical store.
Clean the blister thoroughly and about an inch area of the skin around it.
Puncture the blister and allow it to drain naturally. Do not press initially. Only when much of the fluid has drained can you press with a cotton swab to drain it.
Apply Neosporin or triple antibiotic ointment. Keeping it open will help heal it faster. But if you need to wear shoes, please apply a sterile bandage .
Take Motrin thrice daily. Change the bandage every day.
if there are signs of redness or inflammation around the blister in 24 hours, please see a doctor - you will need oral antibiotics.
I hope this helps.
let me know if you need more information.