Yes, usually a UK personal pension can be transferred to another type of UK personal pension plan (like a self-invested personal pension) and/or a different UK personal pension plan provider. However, it is worth noting that some UK pension providers will not accept US residents as new clients.
There can be a number of benefits to transferring an existing UK personal pension to a different personal pension or pension plan provider. However, it is important to obtain advice from an investment advisor like Florin Pensions before making any decision to transfer. Your current pension may have certain guarantees and benefits which could be lost upon transfer and, therefore, need to be considered carefully.