You cannot reshape a tensor of the shape [1, 1, 3, 50] into [1, 1, 3, 75] as the number of elements differ.
Depending on your use case you could either repeat a subset of the original tensor or use an interpolation method to increase the number of elements e.g. via out = F.interpolate(torch.randn([1, 1, 3, 50]), (3, 75)).