You can withdraw some, or all, of your money at any time. However, you need to leave at least £250 in your ISA or close it completely.
If you choose to close it, you might not be able to open another stocks and shares ISA until the next tax year as you might be in breach of the "one pay in" rule. If you take money out and then open a new ISA (for example, if you take money out of a stocks and shares ISA and use it to open a cash ISA), this will affect your annual ISA allowance.
You do have the option to transfer your current ISA to another provider. We recommend you contact the new provider and follow their transfer process.