Can the ram be replaced even its soldered to the motherboard?
Can the ram be replaced by desoldering it and soldering on new memory?
With the right skills and tools anything is possible!
Sadly, replacing the RAM chips on the logic board here is not something a DIY can do. Between the cost of the tools and parts it would be much cheaper just to replace the logic board Mac mini A1347 (Late 2014) Core i5 1.4 GHz Logic Board.
Frankly, I would just get one of the newer 2018 models with the amount of RAM I needed.