In the end, it's up to you. If you think that your current Antec unit is fine then there isn't any "need". That is, until your Antec PSU blows up and fries your entire PC. At that point, you're not looking just for new PSU but every component as well your Antec PSU fried. New MoBo, new GPU and maybe even new CPU, RAM and storage drives as well. After that has happened, the realization of needing better PSU sinks in. But at that time, it's already too late.
If you have money to essentially replace your entire PC once your Antec unit blows up, feel free to keep your Antec unit. I, however, have dealt with PC hardware over 20 years and know very well not to cheap out on PSU by seemingly saving some money now while spending a lot more when the "budget" PSU fails.
Since the PSU selection in Amazon.in is poor and your budget is small, the best PSU you can get, while still having more than half of money left, is;
Corsair CX750, amazon:
https://www.amazon.in/Corsair-CP-9020015-NA-CX750-Watts-Supply/dp/B00E2TYLCS/
or Corsair CX550, amazon:
https://www.amazon.in/Corsair-CP-9020121-NA-550W-Power-Supply/dp/B01MRW2K79/
Is Corsair CX-series better than your Antec VPxxxPC PSU? Yes.
Is Corsair CX-series equal to Seasonic Focus GX? No.
Corsair CX-series is mediocre quality PSU. Better than your Antec but worse than Seasonic i suggested. Due to that, i'd go with 750W unit since lower-end Corsair PSUs (VS, CX and CXm) are known to act up when load on them gets closer to their max output. With 750W unit, you'd have more headroom wattage wise.
I, personally, wouldn't use Corsair CX-series since i care a lot about my PCs and i won't use anything lower than good quality PSU with my PCs. But due to the poor availability in amazon.in and your small budget, compromises should be made. Corsair CX-series is the best of the worst, without using more than half of your budget.
However, you can afford good quality PSU as well,
Corsair RM750, amazon:
https://www.amazon.in/CORSAIR-Certified-Modular-Microsoft-Standby/dp/B07S4WS5L4/
Is Corsair RM-series better than your Antec VPxxxPC PSU? Yes.
Is Corsair RM-series better than Corsair CX-series? Yes.
Is Corsair RM-series equal to Seasonic Focus GX? Yes.
Corsair RM-series is good quality PSU and i, personally, would go with that PSU. While it does cost quite a bit, that's the nature of things. To get cheap and good PSU, you need to buy two PSUs: the cheap one and the good one. You can not get good PSU with cheap price. (It is so with all things actually, better quality things cost more.)
(If you're wondering how much the Seasonic PRIME 650 (80+ Titanium) costs, that powers my Skylake build, then converting it's price into your currency, we get 18,309.87 INR.)