Or if lazy you can take tram 11 from Bahnhofquai in the front of the main station to the helpfully named Kantonalbank stop (although you want to go to the Nationalbank, not the Kantonalbank).


The huge entrance door looks quite imposing but you can just walk in and go up to the counter, no security checks, speaking English is not a problem, and for 40 francs they will just swap it immediately, no forms or ID needed. They will also exchange any valid Swiss bills and coins to whatever denominations you want (but you can also do this at any Swiss Post office).

In other countries, some or all of the above may be different, but cash is still alive in Switzerland even though cards can generally be used in most places now.