If you plan to trade with RCI, you do not trade a week for a week. You trade HGVC points to RCI. You just call HGVC and ask for your trade and they take from your account, the correct number of points, based on the season and size of unit you're requesting. (ie. 5000 pts for a 2 bd, red season RCI trade) Note: that the number of points they take from you is less than the number of points you'd have used to reserve a similar sized unit during that season.
If you want to trade with SFX, then you are expected to deposit the week you own into SFX. But, there has been some news lately, that you can now use your HGVC points to reserve any HGVC unit and trade that unit within SFX.
Hope that helps