You can select either amendment under PCT Article 19 or amendment under PCT Article 34.
For amendment under PCT Article 19, you can amend only once for claims within a time limit of 2 months from the mailing date of the ISR and WO or 16 months from the earliest priority date, whichever comes later. The amendment should be filed to the International Bureau and there is no fee. There is no subsequent examination process after your amendment in this option. By doing this, you can have the effect of amending claims in every contracting States at once. That is, you can avoid repetition of the same amendment for claims in each country in the national/regional stage.
If you want a positive opinion from the examiner, amendment under PCT Article 34 is what you can try. This is called either Demand filing or International Preliminary Examination, and it costs money. You can amend all parts of your application including description, claims, and drawings. Multiple amendments are possible before the International Preliminary Examination Report is established. Time limit for Demand filing is (i) three months from the date of transmittal of the ISR and the WO; or (ii) 22 months from the earliest priority date, whichever comes later. The Demand should be submitted to the competent IPEA directly.