You're have AMM enabled, so Oracle will manage it for you automatically.
SGA_TARGET will be set to a non-zero value, which means:
Specifies the total size of all SGA components. If SGA_TARGET is
specified, then the buffer cache (DB_CACHE_SIZE), Java pool
(JAVA_POOL_SIZE), large pool (LARGE_POOL_SIZE), and shared pool
(SHARED_POOL_SIZE) memory pools are automatically sized.
You can set it to a non-zero value that is equal to or less than
SGA_MAX_SIZE, so if you need to allocate more memory, just up
ALTER SYSTEM SET SGA_MAX_SIZE = 2048M;
ALTER SYSTEM SET SGA_TARGET = 2048M;
See this documentation section (search for "Enabling Automatic Shared Memory Management") - Read that whole documentation section to gain a better understanding.
As an aside, your
SGA_MAX_SIZE does seem very small.