Add a simple queue using a PCQ to share the bandwidth fairly.
/queue type
set 6 kind=pcq name=pcq-upload-default pcq-burst-rate=0 pcq-burst-threshold=0 pcq-burst-time=10s pcq-classifier=\
src-address pcq-dst-address-mask=32 pcq-dst-address6-mask=128 pcq-limit=50 pcq-rate=0 pcq-src-address-mask=32 \
pcq-src-address6-mask=128 pcq-total-limit=2000
set 7 kind=pcq name=pcq-download-default pcq-burst-rate=0 pcq-burst-threshold=0 pcq-burst-time=10s pcq-classifier=\
dst-address pcq-dst-address-mask=32 pcq-dst-address6-mask=128 pcq-limit=50 pcq-rate=0 pcq-src-address-mask=32 \
pcq-src-address6-mask=128 pcq-total-limit=2000
/queue simple add max-limit=384k/2M name="fair share" queue=pcq-upload-default/pcq-download-default
This assumes your uplink is 384k, and uses the latest default pcq queues.
Hope that helps
Nick.