FortiOS version, upgrade one unit of HA pair

I have 2 x FG300D unit as HA pair (active/passive).

Can I upgrade only the passive unit first to ensure no issue then I upgrade the 2nd unit ?

 

HA StatusActive-Passive [link=https://10.199.99.21/system/ha/monitor][Configure][/link]Cluster NameGV-HACluster MembersSEC-FW02/FGT3HD39XXXXXX(Master)PRI-FW01/FGT3HD391XXXXXX(Slave)