my GPU is AMD Radeon HD 5450 and I don't intend to buy a new GPU even if it would be a better choice but I would like to find out what kind of fan or heatsink do I need to install to it that it might cool it down as it reaches high temperatures even when idle it only has one little fan and since it is an old GPU I'm sure it wont be easy anything to fit so I'm hoping someone here might know.
Sounds like you need to replace the thermal paste on the GPU. When it comes to GPU's there aren't other flavors of heatsinks you can get for a specific model as you would CPU's. You can only get a replacement fan and heatsink, not another variant. Since you say the card is old and is starting to heat up easily, then it's most likely the thermal paste is drying up. Just replace that and it should be fine again.