I urge caution. I tried recapping an old Adcom amp, the right channel in my custom built Tannoys got fried. I hope this doesn't happen to you.
Without a schematic and test equipment you will have quite the challenge. Just like repairing a car, success depends on identifying the problem -- not throwing parts at it. In both cases you need diagnostic equipment to identify the problem and the skill set to know what to look for and interpret the results.
You may succeed, don't get me wrong, but you have to identify everything you replace and make sure direct substitution is given priority over "better quality". To avoid complicating things for you, practice desoldering on old pcb's until you get the pads clean as a whistle without damage.
Work slow, work deliberately. Plan ahead what should be removed first and take plenty of pictures of the board for assembly reference before you remove anything. Check and double check everything before you put the leads through the holes and check and triple check all diode and transistor orientations before soldering.
The don't change any values is critical for keeping original sound, example, if original caps are 85 degrees do not substitute with 105 degrees whatever a technician may say, new caps are much better today. Compare the original factory specs of parts to be changed to new ones, you can create an excel of what to substitute and compare the specs, this will give you a better understanding. Service manual is a must. Each step at a time and rather work at night.
I just did this for the first time on a Sansui 5050. It sounds great. Here is what I learned. Watch a few videos on how to solder/desolder electronics. Watch a video on how to “tin” a soldering iron. You can get service manuals at hifiengine.com. Replacing capacitors is no big deal as long as you use the same uf rating. The voltage can be a little higher. Transistors you need to be careful. Find a direct replacement and make sure you know what prong goes where. (ECB, BCE, etc). Resistors are easy but the coloring on the outside that tells you the resistance might have faded making it hard to know the resistance. These shouldn’t go bad and I’d leave alone. (Unless the service manual identifies the resistance). After each circuit board I would test with a “dim bulb” tester. (Easy to build). This will tell you if there is a short and you will know what board it is on.