Do you want to replace the running rigging because it is worn and frayed? How old is it? Is it run inside the mast or outside? Is it all rope or wire/rope combination. These can be reasonable considerations - you might not need to replace the running rigging if it isn't showing signs of wear, for example. If it's all rope, can you see UV damage?
I would assume that the running rigging that you already have on the boat has been adequate. So sizing would not change, so just buy the same size again, unless you want to replace all-rope halyards with wire/rope halyards, for example. As far as what kind of line to buy, most suppliers of line have good information on their web sites, for example, New England Ropes
The type of halyard line that you buy is, to some degree, dependent upon whether you are planning on racing, and thus need the best quality halyard line possible, with as little stretch as possible. Or wire/rope combination. Price.
And, in my opinion, ease of splicing. So for us, we used high quality polyester double braid from New England Ropes, not parallel core lines such as Sta-Set X(tm), for example. (Peter got a very good deal on Sta-SetX one year, and I had to splice it without instructions; the first two eye splices I did were pretty tough until I figured out how to do it. But I cursed it the whole time I was doing the work!)
If you cannot do your own splicing (I think it's pretty easy, though I always have the instructions in front of me when I splice double braid) then please pay a professional to do the splicing. Do Not Use Knots to attach shackles to your halyards. Do Not. Do not use knots on any of your running rigging.
Richard is right that your standing rigging should be checked and perhaps some of it replaced. The standing rigging is more important - it's what keeps that expensive mast up. How old is the rigging? How hard has the boat been sailed with this rigging? For this I would hire a professional.
If your mast was down inspecting sheaves and blocks would be easier than if somebody has to go up the mast to inspect it all, but you can probably do that yourself, even if you decide to hire a professional to re-inspect it and do the work.
Another one, in Riviera Beach, FL is Florida Rigging & Hydraulics