For Access Accounts and Notice Accounts, you can make as many withdrawals as you like - there are no limits.
For Fixed Rate Bonds, withdrawals are not permitted.
For Fixed Rate Cash ISAs, partial withdrawals are not permitted; you can only close or transfer the ISA in full, subject to an 'early access charge'.
Remember, if you choose to close the ISA and have your funds returned to you, the funds will lose their tax-free status. You can find details of the 'early access charge' in your Product Specific Terms and Conditions.