Absolutely possible, infact id say its easier than going from a 6 to 8. definitely make sure you have grade5/ foundation stuff down great. losing marks there will hurt you. online, search up grade 6-7 questions and grade 7-8. 7-8 is more accurately grade 7 level ive found. Other user mentioned corbett maths, and maths genie, esp corbett maths questions on specific topics. Sparx ive heard is great too, to find those are great, but straight up, pass paper questions. LOADS of past paper questions. then its less likely you will come across a question type youve never seen before. One great tool is OnMaths. They do mini predicted papers, and show where your loosing marks in comparison to how many marks you couldve potentially gotten if i remember correctly.
On Maths:
https://www.onmaths.com/mock_exams/?archiveType=half_predictionIn exams, little tip, if you do any mocks or just an exam by yourself, or even the real thing, imo the golden rule to make sure youve secured a grade, is to do (10 x (your grade)) - 15. so in this case, 45 approximately for a 7, and thats a solid effort. During tests, if you have time, count up presumed marks, itll help with working out how much you need to get a grade. single handedly boosted my grade from a 5 to 6 and sometimes 7. bare in mind, 45 is lowkey pretty harsh, especially in regards to last years papers (1 was easy, 1 was meh, 1 sucked, and this is a shared opinion from what i know), so if you get anywhere near that, then your in the running for a 7. Wish you luck, hope you get that 7.