Ich räume wöchentlich mein Zimmer auf.
This is correct. Starting from here, there are several options to indicate other intervals:
You could say zweiwöchentlich, dreiwöchentlich etc., which means that you perform the activity once every n weeks. However, these words sound quite formal and are mostly used in written announcements such as "Die Zeitschrift erscheint zweiwöchentlich.", "Die Veranstaltung findet dreiwöchentlich statt."
The same works with other intervals, as well:
- zweimonatlich means once every two months
- zweijährlich means once every two years
n-mal pro Woche; alle n Wochen
This expression can be used in all contexts and is also somewhat more flexible than the above one:
- If the frequency of the described event is higher than the reference interval (e.g. a week), you can say dreimal pro Woche (three times every week).
- If the frequency of the described event is lower than the reference interval, you can say [einmal] alle drei Wochen ([once] every three weeks).
- Lastly, you can also express other intervals like this, e.g. fünfmal alle zwei Wochen (five times every two weeks).