raising soil level around plants... how?

I'm in need of raising the soil level on my little boarders about 4" to 6" to match the level of the rest of the garden area...
on on. Boarder I have lavender and 3roses.
the other I have an assortment of tulips some spent, some just finished flowering and some still flowering.
to what level can I raise the soil above these? The tulip bulbs are pretty shallow but would it suffocate any plants adding it around their bases?
Or am I better digging them out and re planting everything once the soil is levelled?

 

Dependant on how many plants you would need to move, I think I would go down this route personally. You can then re-site everything where you want them and not necessarily where they were.