Let's explode a major misconception first: buying a new router with fancy new wireless technology won't necessarily get you better speeds. Whatever equipment is connecting to, it also needs to support that fancy new wireless technology, effectively eliminating most smartphones, consoles, media streamers and a good swathe of laptops, too. If your phone only supports 802.11b/g, then 802.11ac ain't gonna help you much.
It's also worth ignoring the big number on the box. No single client will ever see the advertised 300/450/600/750/900/1300Mbps, as that's the total capacity of the router for all connected devices. Actual speed per device will vary massively, depending on the environment, capability of the wireless receiver and antenna configuration inside the device. To give you an idea of best-case scenario, the fastest speeds we've measured on 802.11n 2.4GHz, 802.11n 5GHz and 802.11ac 5GHz are 139Mbps, 205Mbps and 537Mbps, respectively. 802.11ac is awe inspiring, but barely anything is available yet that can actually receive that signal.
So, let's see how you can improve your current situation with minimum spend.
Move your router
A pretty simple solution, but effective. Try to make sure it's in the centre of your coverage area, and keep it off the floor. Try to make it as exposed as possible — stashing it between a cupboard and a wall is asking for trouble.
Check your channels
In particular, 2.4GHz Wi-Fi is incredibly popular, and where most interference happens. You can mitigate this by changing the channel that your router uses. This slightly changes the frequency, and, with any luck, will improve signal strength.
Many routers these days select channels automatically, but if you'd like to tweak a little more, a program like InSSIDer can help you see what wireless channels are occupied in your area. It'll change as you wander around your house, too, depending on how close others are living and where their routers are.
A typical 20MHz 2.4GHz signal can bleed up to two adjacent channels on either side of your chosen channel as well, so try to choose one that's as clear as possible. Usually, this factor makes channels 1, 6 and 11 the better choices, but only if they're not heavily populated already.
There is an OS X version of InSSIDer; however, unlike the Windows version, it's not free. Mountain Lion has a basic Wi-Fi scanner built in, or you could try iStumbler.
Double your bandwidth
Although it's not friendly to your neighbours, if you really want to get a stronger 2.4GHz signal, turn on 40MHz mode, instead of just plain 20MHz. See that big yellow line in the InSSIDer graphic above? That's a 40MHz signal, straddling channels and dominating the 20MHz signals.
If you've got a router that's capable of dual-band wireless, it might be worth checking out the 5GHz band. While range is noticeably shorter, it typically avoids interference issues by having non-overlapping channels, and should perform better at closer range. On many routers, you can run 5GHz simultaneously with 2.4GHz to keep everyone in the house happy across different devices.
If you're using an older laptop (three to five years), have done all of the above and still haven't seen the improvement you need, the next-cheapest option is to change your Wi-Fi Dell Inspiron 1525 Adapter.
While many laptops will take standard, internal mini-PCI-E adapters, if you're game enough to open them up, be aware that vendors like HP do have a habit of white listing. That is, only allowing specific adapters to be installed in their laptops. This is quite annoying if you've just picked up a top-of-the-line Intel Centrino Ultimate-N 6300, and it doesn't work.
A safer alternative is to get yourself a high-end, dual-band USB dongle for around AU$100.
OK, it's time to look at new equipment
If you're still not doing well, it's time to look at new equipment. While there are a few hardware solutions to extend your range, our favourite is to get a new, more powerful router, and to put the old one in a wireless black spot, with an Ethernet cable joining the two. If you find wires a bit unsightly, you could always pair this technique with power-line networking to hide the mess.
When set up, give both wireless networks the same name and password, and your wireless devices should roam to whatever signal is strongest.