METOPROLOL ER SUCCINATE 100MG?

my mom is going from 50mg of Metoprolol Tartrate (1/2 tab bid) to 100mg Metoprolol ER Succinate; her lisinopril also increased from 5mg to 10mg qd; Going up that much on the Metoprolol scares me, can I cut the Metoprolol ER tabs in half since they are extended release?? Her regular doctor did not change her hypertension meds, her neurologist did because I told him her BP had been high and headaches were frequent. Cant get in with regular Dr until July. Thanks.