When should I change my JioFiber plan?

[SRoy]

Currently I have the ₹699 - 100 mbps plan (₹824 w GST). I pay for it monthly however the plan shows 3M, not sure how that works.

I want to change it to the ₹399 - 30 mbps plan. However it says I have to play ₹470.82 in advance. So, I have some questions regarding that:

• Will I have have to pay the advance plus the actual price of the plan Or does the advance already cover it?
• Do I pay it before 30th of this month before the bill expires?
• Does it take time to apply? - It says the plan will be effective in 24 hours, so I won't have internet for a day?
• Is it better to call jio personnel who installed the jio router?

Thanks a lot for taking the time to read this.
I hope I get some answers and understand what to do better. And if the speed is too low for me, hopefully I'll be able to switch it back the same way.
I'll provide some screenshots below so it's easier to understand.

 

[Lolita_Magnum]

The plan usually changes immediately, sometimes takes a day.
Your advance amount goes as credit and is not really charged.

Your final bill will be prorated, and the standard 399+GST after that.
The credited amount is settled, once the bill is generated as per date. 21st in your case.