imac wirless

[itsrron]

sometimes my wireless connection drops low which is not out of the ordinary BUT when it does and i click on the Airport icon to search for more connections i seem to only have mine and no others. Surely this cannot be a side effect of poor connection as the other connections should still appear but mine should just be lower down the list no???

Could it be due to overheating? what if i download that app form apple that enables N-wireless connectivity

also where is the wireless located on an imac and is it hard to replace?