Increase Accuracy on Keras Multiclass Classifier
You should understand if the model you built is able to learn from the data. Therefore, plot the accuracy and the loss for both training and validation set versus the number of epochs.
Then, if the model needs more epochs, give it more epochs. Otherwise, try different optimizers, activation functions, number of neurons, number of layers, and batch size.

From the (flawed) plots you provided (please, plot accuracy for training and validation on one graph, and loss for training and validation on another graph), you can see two clear phenomena:

accuracy stops to increase after a very few epochs;
loss curve is unstable.

which suggest that the model does not learn from the data (I would start off with a shallow architecture, tuning number of neurons, trying different optimizers, activation functions, and then number of layers) and the dataset could be unrepresentative.