Fix slow Wi-Fi with checks in the right order

Help me fix slow Wi-Fi.

What's slow: [whole house / one room / one device]
Devices affected: [list]
Router age if known: [details]
Have I restarted modem and router: [yes/no]
Speed I pay for if known: [details]

Ask me up to 3 short questions first if anything important is missing. Wait for my answers.

Then:
1. Ordered checks (restart order, distance, congestion, guest network).
2. What to test on one device next to the router.
3. What to ask my ISP.
4. When a hardware change is worth considering — without naming a product to buy.

Only use what I've told you, leave blanks for anything I haven't given, and don't invent facts, steps or official URLs you're not sure of. UK English.

Stay in this ChatGPT chat. Do not turn on apps or connectors, and do not use memory from another chat.