I generally agree with what has been said here, especially with regard to Sunnyring's comments about the effect that trying to do this yourself will have on you.
I will add that if I was in your position, before the decision that he needs to be put down was made at all, I would want to be certain that you can answer yes to all the following questions:
1) Has the cause of his seizures been properly investigated, and is it understood so far as is possible? (Seizures in birds, as in humans, can have many different causes, and so it is very difficult to make accurate prognoses without knowing the cause.)
2) Is his condition not treatable, or has all treatment which could be reasonably expected to work in his case been tried and failed?
3) Is his condition progressive in nature? (This has not been established unless question 1 has been answered to the extent that some sort of named diagnosis has been made - guesses, even well-educated guesses by professionals, do not cut it, especially if the professional in question is not an expert in neurological conditions.) This is to say that it can be expected to continue getting worse, with no hope of remission or alleviation of symptoms by treatment, or of the condition stablilizing or improving by itself.
You don't give details of his condition or what the vet said about it, so it's not clear to me (or presumably anyone else posting here) which category he fits, but if you cannot answer a definite yes to all the points above, I want to draw your attention to this, which I think is important to consider for anyone who has an animal which suffers seizures:
Most humans (and animals, so far as we have any way of telling) who have seizures do not suffer severely during the actual seizures - many humans who have seizures are not even aware of what is going on at the time, and have to be told later by others what actually happened, so we can assume something similar for animals. Seizures can point to severe underlying conditions such as deteriorative genetic illnesses, brain tumors, late stage organ failure, or poisoning - in which case euthanasia is likely the best option for an animal where the actual cause cannot be treated sucessfully. However, in cases where the seizures themselves are the main problem (eg. many cases of epilepsy), the animal is unlikely to be suffering much if at all during the actual seizures - the main danger to its well-being is therefore from associated threats such as injuring itself through accidents while seizing (eg falling off its perch in the case of a bird), or suffering hypoxia leading to brain damage, which can happen as a result of recurring or prolonged seizures. In these cases I think it is important to weigh carefully whether the animal can still be given a fulfilling quality of life by its carer despite the seizures, and to remember that in many cases it is more traumatic for the carer to witness the animal having seizures than for the animal itself.
Many animals (not to mention humans) who suffer recurrent seizures are in fact capable of living fulfilling, and often long lives even where the seizures are not fully controlled, besides which, many potential seizure causes are treatable, and in some cases completely curable.
