Here's a rundown of your options (and I added a note difficulty and knowledge):
Option 1: Hard wire your house. Best performance option overall, heavily labor intensive. If you opt for this, plan ahead and make sure you run extra wires to every room and leave them coiled for future expansion. This option is probably best anyway if you have a lot of other wireless networks nearby causing channel congestion.
Option 2: Add a repeater to your current wireless setup. This is the best option for wireless coverage, but would at least require you to know how to set up your devices correctly or take them to someone who does know. If you have to get outside advice, you can pay Best Buy to come do it via Geek Squad, or take them in to a tech shop and have them configure them properly. To repeat 802.11n with maximum effect, you have to have a pure-N network, which prevents you from using any older 802.11a/b/g devices on your network. This is the easiest option to have set up if you know nothing and don't mind paying someone else for that knowledge. The downside is that if you ever have problems, you have to pay for that knowledge again.
Option 3: Router hardware upgrades. You could possibly upgrade the antennas or even replace the router itself with a better one. This option would be most ideal if you have a cheap consumer-grade router and wish to upgrade to a more powerful business-class dual-band router. This option can be expensive, but generally will produce good results. If you have a recent model quality consumer grade router, this option is likely to waste your money. Keywords: recent model and quality
This is fairly easy to accomplish as a DIY, but if you're just following the instruction booklet that comes with the router, this won't guarantee better results. Again, you may end up paying for knowledge.
Option 4: Relocate your router. Generally speaking placing your router in a far-away corner of the area you're trying to cover is not an efficient solution. Placing the router in a central area (and adjusting the antenna or floor to maximize broadcast area) will result in a better signal coverage. Good news is this is the easiest option you can do yourself, and unless your house was built like a bomb-proof bunker (concrete floors and walls with steel rebarring) this will probably make the most noticeable difference. Make sure you keep the router away from other radio-frequency emitting devices to help signal coverage.
Option 5: Router firmware changes (firmware is the programming built into the router...similar to an operating system on a computer in some ways). Depending on the model of router you have, you could upgrade the firmware to an open platform such as DD-WRT or Open-WRT. These unlock a whole host of options you can get yourself in trouble with, and the process to upgrade the router can potentially destroy it in the process.
Not an amateur move to make, this can possibly give you amazing results if you have the right model router. Or it can give you nothing but trouble. That's very model dependent. Definitely one of the more knowledge intensive options, but a good way to squeeze every inch of performance from your router.
Option 6: Change your broadcast mode. 99% of people think that because they have an 802.11n router, they have an N network. This is simply untrue, as most routers are set up to make a mixed-mode network that offers 802.11a/b/g compatibility. Setting your router to N-only and configuring your devices correctly will directly increase your network performance. Pure-N networks have a "dome" of coverage that's smaller than older standards, but anything within that "dome" is going to connect and do fine, regardless of signal strength. The downside here is that non-802.11n devices are effectively locked out of your network. This is relatively easy to do in most router interfaces. Advanced users can also set up subnets that support legacy devices, but not all routers allow this option with the stock firmware.
Overall, there are other options that exist, but they're mostly variations on these 6. If you tell me what model and revision of the router you use, I can probably be more specific to your options.