It is possible to use > to indent only one line one level, but it is better to use == that indent the line to the correct level according with your tab settings.
You can use = (single instead of double) with a motion, then you can do like 40= and indent the next 40 lines.
To indent the entire file you should use gg=G. That is gg to go to begin of the buffer, =G to indent till the end of the buffer.
You can also map it to a key using marks functionality to put the cursor back where it was before indent:
<Leader>i mmgg==G`m<CR>`Where: mm drop a mark where the cursor is at when the key is pressed. Then indent from the beginning till the end of the buffer. And then use `m for going back where the mark was dropped.