frame

My what I was told is a rim board(the outside wood frame) of my house is rotten or eaten up by termite. I would like to know how I can replace frame?

Not a good first time DIY job.
Have you had the house treated for termites yet? Do not let someone try and cheat you with those cheap plastic tubes around the house, there a rip off and you have active termites and need a chemical treatment.
The siding needs to come off in that area, the old rim joist gets pulled out by removing all the nails going into the floor joist, then just replace it.
If it's a brick house or the damaged area is behind a deck, stoop or porch then things get real fun and expencive.

Yes brick. I went under and entire front board is damaged. Gaps in between hardwood floor and baseboard inside in living room. Real bad at doorway.

Then your limited on options on this one.
You can bet your foundation plate is also shot and this is what the rim joist is sitting on. Years ago there was no requirement to have the foundation plate to be pressure treated, some counted on an alumium "termite shield", well the termites come up inside the concrete block eat through the wooden foundation plate and the aluminum has corroded, has missed places around the holes for the foundation bolts or there is none then there free to eat there way into the house.
Anytime I see a brick and block stoop, deck, or porch right up tight to a house that's first place I'd look for termites. Often time workers would back fill it with scrap wood, broken block and brick anything laying around so the termites have easy digging and food along the way.
The two choises you have is to remove the damage areas from the outside, or inside.
The outside you would have to cut back or distroy the stoop, remove the brick before you could even reach the damage area.
The second choise is to come from inside, and this is not going to be a DIY job.
The floors have to come out, a beam made to support the roof and lift it slightly from inside the house, floor joist removed, then you can get to the foundation plate and rim joist.
Hopefully someone else will come up with some magic way to do this but I do not see that happening.
We have had to do this on lots of homes from 7 to 120 years old homes.
There's going to be people making suggestions on how they would do it or how there cousins best friend second removed did it. But ask yourself have they ever done this before or are they just guessing how to do it.