How to fix this MemoryError: Unable to allocate in Python

Here is the code I have

out = out.T.groupby(level=0, sort=False).sum().T

and it gives this error

MemoryError: Unable to allocate 13.1 GiB for an array with shape (37281, 47002) and data type int64

I tried this

out = out.T.groupby(level=0, sort=False).sum().astype(np.int8).T

but still getting the same error!

Any idea how to fix it?