In a fixed exchange system, currencies are fixed by the central bank of each country. Note: Relieving upward pressure is easy enough, from simply selling the domestic currency, increasing supply and decreasing the value of the currency.

Official reserves

Buying domestic currency with foreign reserves simulates an increase in demand which generally alleviates downward pressure of depreciation. However, it may be unsustainable for long-term downward pressure. Relieving upward pressure is easy enough, from simply selling the domestic currency, increasing supply and decreasing the value of the currency.

Increase Interest rates

Attracts foreign investment, which increases demand for the currency. The downside is how this is exactly a contractionary Monetary Policies.

Limiting imports

Similarly, this will reduce the supply of the domestic currency, which can exert upward pressure on the value in opposition of the downward pressure. However, this involves contractionary policies again, or trade protections and their disadvantages. Arguments against trade.