browse to the specific space you want to version all content. then create a rule that versions all content. here's how step by step:
1. browse to the particular space
2.click on "more actions" then select "manage content rules"
3. click on "create rule"
4.under select condition, select "all items" and click on "add to list" and click next
5. under select action, select "add aspect to item" and click on "set values and add"
5. under set action valuables, select versionable and click OK. proceed by clicking next
6. type should be inbound and give it a title
7. select run rule in background and you are done
every item that you upload into that space will be versionable.
tell me if you need more help.