Find each replacement resistor and make sure that you know where each resistor goes. Finding old resistors can be difficult, so the modern cylinder type with the colored bands can be substituted. Old resistors did not always use the modern colored band system; often, the value was simply stamped into the resistor. These old marks can be tricky. On antique resistors the letter "M" often means 1,000, not 1 million. This was consistent with "M" for "Milli." Another mark on old resistors that is confusing is the use of "W" for "ohms." A schematic for the specific radio you are working on will provide the best information about resistor values. Antique radio schematics are available on the Internet. If you do not have a schematic, do a thorough exploration of the radio and mark down the value of each resistor.
Join modern resistors serially or in parallel to obtain the desired resistance. You might not be able to find a 450 ohm resistor, but you can get the equivalent resistance by attaching a 50 ohm and a 400 ohm resistor in series. You may not be able to find a 33 ohm resistor, but you can get the equivalent resistor by attaching three 100 ohm resistors in parallel.
Remove the old resistors from the radio. For each resistor, clamp something like a clip of clamp (as a heat sink to protect the radio) to the terminal that the resistor is attached to. Heat the solder and remove one end of the old resistor physically. Do the same with the other end of the resistor. Clean off the terminals. Physically attach each end of the new resistor in place with the needle nosed pliers. Make sure the heat sink is in place and solder both ends of the new resistor in place.