Looks like Hydrangea 'Annabelle'. Like them all it doesn't like to dry out so a good fertile well dug piece of ground and some good compost incorporated and well mixed in at time of planting. Flowers are so large that in its early years it may require support, but after a few years it is a robust and surprisingly tough plant. Plant in a site away from the hottest sun (the best I've ever seen are in Winchester on the north east side of Peninsular Square properties, sheltered, but little direct sun. They're huge). Pruning is done in February, when you cut right down to the ground for strong growth to be produced from the very base. You may well see the new buds forming already by then. The flowers are produced on the current season's growth.

Thank you for your reply. Do you think I can move it to another part of the garden? We need to dig for gas pipes, and workers will remove it :(
When is the best time for moving? if i can possibly save it . thank you

If it has to be moved, then as late in the year as possible, so the plant doesn't suffer too much from stress brought about by the move and inevitable root damage. Water it well first a few days before hand (a bucket or two), then dig it up with as much rootball as you can preserve and plant it in its new spot immediately. It means getting the new site prepared first, therefore. It shouldn't mind too much, and cutting off the flowers (just the flowerheads) will also lighten the load on the plant's resources.