Remortgage - legal advice

Hello,

My fixed rate deal is due to end in March, and I'm considering whether to remortgage or go onto the bank's SMR. If I remortgage either with my existing provider or a new one, do I need to retain a solicitor and/or get another valuation?

Sorry if it's a bit of a stupid question, but it's my first mortgage and first time remortgaging so I'm a bit clueless :)

Thanks!