Download speed is decided by the slowest link in a chain, and it is usually not the one people change first.
The chain
Your plan. The ceiling. A 10 Mbps line tops out near 1.2 MB/s no matter what else you do — a 1 GB file takes about fifteen minutes at best.
Congestion. Evenings, roughly 8pm to midnight, are the worst hours on most Bangladeshi networks. The same file often pulls several times faster in the morning.
Wi-Fi. Distance and walls cost more than people expect. Being in the next room can halve it; 5 GHz is much faster than 2.4 GHz but carries a shorter range.
Your device. An almost-full phone writes slowly. Below about 2 GB free, storage itself becomes the bottleneck.
The file. A 4 GB download is not slow because it is slow — it is four times a 1 GB one.
What actually helps
Download at off-peak hours. The single biggest difference for most people, and it costs nothing.
Move closer to the router, or use a cable if the device takes one.
Use a download manager that resumes. On a connection that drops, this is the difference between finishing and starting over — and restarting spends the data twice.
Pick a smaller file. 720p instead of 1080p roughly halves the wait, and on a phone screen the difference is hard to see.
Free up storage first. A download that fails at 90% on a full device wasted all of it.
What does not help
A VPN makes downloads slower, not faster — it adds a detour. Use one to get around a block, never for speed. “Speed booster” apps cannot exceed your plan; nothing installed on a phone can. And restarting the router helps only if it had actually locked up.
If it stops partway every time
That is the connection dropping, not the file. A resuming download manager is the practical answer — it picks up where it stopped instead of throwing away what you already paid for in data. If it always fails at the same point, start it again on a different network.