just take it to the rspca or similar if you cannot look after it, else find it a home with someone else.. bear in mind that you will not be able to get the dog back.. unless you have a good friend/family member who can look after it.. but i dont think its fair on the dog to keep changing owners.. if it was me id give it up as sad as it may be..
Sorry but if you don't mind me asking, why can't you keep it? Can't you try to keep it at least? It's so unfair on an animal to just chuck it around all over the place. I strongly recommend you find a trusted family member/friend to look after it - although the RSPCA are there for homeless animals, they are not rich and full of resources. Also, they can be quite distressing for a lot of dogs - I got my dog from there and she has always had a very strong, confident personality, but even she was petrified in there. They are surrounded by other dogs in caged-in areas, and although they get walks and human attention,it's not ideal for them.. so please only leave your dog there if it is the final option you have.
If you gave the dog to a home you likely wouldn't be able to get it back, as well as it not being fair on the dog. You may have to plead with a family member to look after it for the year, but you would have to think about them having to walk it daily and the costs of dog food...
I don't mean to be rude but can I ask whether something has come up suddenly or did you not foresee the situation at the time you got your dog?
Dogs are wonderfully faithful creatures who get extremely attached to you. It's very hard on them but if you are gonna give it up better now than later. It'd be better if you found a nice home for it than give it up to shelter.
It takes quite a long time for dogs to become fully attached and comfortable with owners and passing them to different people isn't fair to him/her. Although it'll be hard offering him/her to someone who can take care of it full time is more fair to the dog itself.
You really need to make the effort to ensure your dog is going to be cared for and loved.
It's been mentioned above that dogs become extremely attached to their owners, and he/she will wonder what he did wrong if you give him/her away. If you have no other choice, then so be it, but please ensure your dog will go to a loving new owner, or the RSPCA as a LAST resort.