Certainly looks like a case for a macro

• /array<CR> to jump to the first array
• qq to record the macro into register q
• de to delete the word array
• ma to save the cursor position on the first bracket at mark a
• %r] to jump to the matching bracket, replace it by another bracket
• `ar[ to jump back to position a and replace that bracket
• q to end recording of the macro

After that, it's just repeatedly pressing n to jump to the next match and @q to play the macro. You could make the search part of the macro and just execute until it stops, but I thought you might prefer to visually check each substition... you choose :)

Certainly looks like a case for a macro

• /array<CR> to jump to the first array
• qq to record the macro into register q
• de to delete the word array
• ma to save the cursor position on the first bracket at mark a
• %r] to jump to the matching bracket, replace it by another bracket
• `ar[ to jump back to position a and replace that bracket
• q to end recording of the macro

After that, it's just repeatedly pressing n to jump to the next match and @q to play the macro. You could make the search part of the macro and just execute until it stops, but I thought you might prefer to visually check each substition... you choose :)