BIP 148 is due for activation on the first of August.
If your exchange doesn't support BIP 148 by late July you need to get your BTC out and into your own paper or software wallet where you are the keeper of the private keys.
Failure to do this could mean that your BTC will not be registered and validated with segwit and may be unusable.
No one knows for sure yet how this will go so probably the safest route is to pull your BTC out of exchanges until after BIP 148 is activated.